Dissertations / Theses: 'Ultramafics'

1

Ramos, Rodrigo Chaves. "Complexo ofiolítico Arroio Grande, sudeste do Escudo Sul-Rio-Grandense: caracterização e discussões das unidades ortoderivadas." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2014. http://hdl.handle.net/10183/94680.

Full text

Abstract:

O presente trabalho é a continuação das pesquisas anteriores relacionadas às rochas metamáficas e metaultramáficas da região de Arroio Grande, sudeste do Escudo Sul-rio-grandense. A partir de estudos de campo, microscopia óptica, microscopia eletrônica de varredura e difratometria de raios X, essa associação de rochas (anfibolitos, serpentinitos cromíferos, xistos magnesianos, micaxistos, quartzitos e mármores) foi interpretada como possíveis fragmentos de crosta oceânica relacionados ao encerramento de um paleo-oceano durante o ciclo orogênico Brasiliano/Pan-Africano no Neoproterozoico e denominada de Complexo Ofiolítico Arroio Grande. Nesta dissertação é apresentada uma breve descrição deste complexo ofiolítico e o seu contexto geológico, além de breves considerações sobre sua importância do ponto de vista da evolução do paleocontinente Gondwana Ocidental durante o Neoproterozoico. Em seguida, é apresentado o artigo denominado “Geologia da associação metamáfica-ultramáfica da região de Arroio Grande, sudeste do Escudo Sul-rio-grandense”, aceito para publicação no periódico Pesquisas em Geociências da Universidade Federal do Rio Grande do Sul, no qual são caracterizadas as unidades metamáficas e metaultramáficas do referido complexo. Tais pesquisas têm como principal objetivo adicionar novos dados aos já existentes na literatura, aquecendo as discussões acerca da existência ou não de possíveis ofiolitos na porção oriental do Escudo Uruguaio-Sul-rio-grandense relacionados à ocorrência do paleo-oceano Adamastor, e dos modelos evolutivos para a reconstrução do paleocontinente Gondwana Ocidental. The present work is the continuation of previous researches related to the metamafic and meta-ultramafic rocks located near the town of Arroio Grande, southeastern Sul-rio-grandense Shield. Through fieldwork, optical microscopy, scanning electron microscopy and X-ray diffraction, this rock association (amphibolites, chromian serpentinites, magnesian schists, mica schists, quartzites and marbles) was interpreted as possible slices of an oceanic crust related to the closure of a paleo-ocean during the Brasiliano/Pan-African orogenic cycle and called Arroio Grande Ophiolitic Complex. A brief description of this ophiolitic complex and his geological setting is presented in this dissertation, with brief considerations on their importance, from the point of view of the Western Gondwana paleocontinent evolution during the Neoproterozoic Era. Subsequently, the article entitled "Geology of the Arroio Grande meta-mafic-ultramafic association, southeastern Sul-riograndense Shield”, accepted for publication in the Pesquisas em Geociências Journal of the Rio Grande do Sul Federal University is presented, where the metamafic and meta-ultramafic units of the aforesaid complex are characterized. Such researches have as main objective to add new data to existing literature, promoting discussions about the possible existence of ophiolites related to the occurrence of the Adamastor paleo-ocean in the eastern portion of the Uruguaio-Sul-rio-grandense Shield and about geologic evolution models for the reconstruction of Western Gondwana paleocontinent.

APA, Harvard, Vancouver, ISO, and other styles

2

Bettarini, Isabella. "The nickel hyperaccumulating plants of genus Odontarrhena (Brassicaceae): novel insights from molecular, physiological and biochemical analyses." Doctoral thesis, Università di Siena, 2021. http://hdl.handle.net/11365/1128453.

Full text

Abstract:

Due to the high nickel concentrations, serpentine soils provide a very restrictive and selective environment for plant life. Some plants, termed “Ni-hyperaccumulators”, are adapted to live on these heavy-metal-enriched soils without toxicity symptoms. Ni-hyperaccumulators are increasingly important for research on metal tolerance, homeostasis and biotechnological applications. This project aims to investigate nickel accumulation in taxa and populations of Odontarrhena, a genus of tribe Alysseae (Brassicaceae) that includes over 85 species many of which are Ni-hyperaccumulators. Based on a previous systematic study conducted on poorly-known populations of Odontarrhena native to Albania we performed a molecular study to characterize taxa and populations of this genus. To this purpose we used DNA sequencing and the AFLP-fingerprint technique to reconstruct the species phylogenetic relationships and the population differentiation patterns in relation to their distribution, ploidy level, intensity of anthropic site disturbance, altitude, soil type and metal concentration population (Ni, Cr, Co, Ca, Mg). We found significant population differentiation, dominance of within-population variation, no isolation by geographic distance and existence of six genetic groups variously represented across the six taxa possibly due to hybridization especially in disturbed sites. Next, we compared metal concentrations in native Odontarrhena populations from Albania in relation to their soil of origin. We determined the concentration of the most important trace metals (Ni, Co, Cr, Mg, Ca, K, Fe and Mn) in soil, plant roots and shoots of five taxa from 20 different outcrops. We found large differences in mineral element concentrations in soils and also between the plants; shoot Ni concentrations in Albanian Odontarrhena taxa depend on soil Ni concentrations but not on species identity. For O. chalcidica, the most widely distributed species, this “environmental fingerprint” was found not only for Ni, but also for Ca and Mg. After these investigations on native populations from the natural environment, we designed an experimental study in controlled conditions. Plant seedlings of seven taxa and 11 populations of Odontarrhena from serpentine and non-serpentine sites of the Balkan peninsula and Italy were cultivated in hydroponics with increasing NiSO4 concentrations to determine plant growth and Ni accumulation. These plantlets were analyzed to test inter- and intra-specific differences in nickel tolerance and accumulation, in relation to Ni levels in the soils and in wild plants. We found a metal stimulatory effect on growth that was present in the low-dose zone and significantly fitted the Brain-Cousens hormetic model. Taxa showed broad variation in tolerance, with the most tolerant plants requiring the highest Ni concentration for optimal growth. Our data suggested that tolerance is associated with hyperaccumulation ability. Among the obligate and facultative serpentinophytic species of Odontarrhena that have been investigated we found a notable exception, O. sibirica, a facultative serpentinophyte in which accumulation ability was enigmatic from previous studies. We addressed this issue using observational and experimental methods as in our previous researches. We found that Ni-concentrations in the native populations sampled on serpentine soils in Greece were always much lower than the hyperaccumulation threshold. When cultivated together with other Ni-accumulating Odontarrhena species on the same natural ultramafic soil, O. sibirica was the only one unable to accumulate the metal. When grown in hydroponics at different NiSO4 levels Ni-accumulation occurred only at higher concentrations which, however, had a toxic effect. This peculiar combination of Ni-response traits could be the result of a partial evolutionary loss of ability with respect to all other Ni-accumulating congeneric species. For its unique characteristics, O. sibirica could therefore represent a unique model system for further studies on the evolutionary dynamics, physiological mechanisms and genetic control of metal accumulation and homeostasis. In a parallel study, we investigated photosynthesis responses of the same plants using an experimental approach. In non-hyperaccumulator plants, toxicity symptoms to above 10 μg g-1 DW nickel concentrations in soils can include inhibition of photosynthesis, impaired nitrogen assimilation and disturbed enzyme activity. However, there is a complete lack of information about how Ni-hyperaccumulators reconcile that extraordinary amount of metal in their shoots with an efficient photosynthetic activity, or at least on which photosynthetic parameters the excess of Ni impacts less in these plants. We measured Ni effects on growth, root and shoot metal accumulation and several photosynthetic parameters, such as gas exchange, chlorophyll fluorescence analyses and pigments content in three Odontarrhena taxa (two hyperaccumulators, one not) grown in hydroponics and exposed to three NiSO4 treatments. We found that Ni-hyperaccumulators species are photosynthetically more efficient under Ni excess in respect to the non-accumulating species. In fact, Ni treatment in O. chalcidica increased not only the photochemical efficiency of PSII and the CO2 assimilation rate, but also the stomatal conductance. Finally, this project focused on the determination of the activity of the enzyme urease, the only Nimetalloenzyme known so far in plants, in selected Odontarrhena taxa. The hypothesis to test was whether the high basal requirement for this micronutrient in these plants could be linked to a depletion of the Ni cytosolic pool at low external metal concentration, due to hyperaccumulation mechanism and impairing urease activity. To this purpose, enzyme activity and Ni shoot concentration were determined in plants of accumulating and non-accumulating taxa of Odontarrhena cultivated on Ni-rich serpentine soil and on garden soil, as well as in samples of O. bertolonii cultivated in hydroponics at increasing Ni concentrations. Odontarrhena hyperaccumulators showed similar urease activity when grown on both kinds of soils, with no relation between the enzyme activity and the leaf Ni accumulation. Contrarily, clear indications came from the experiment in controlled conditions, where the presence of Ni determined a progressive stimulation, in respect to control samples, of the activity of the enzyme, associated with an increase in shoot metal concentration. A significant relationship was found between the levels of urease activity and the amount of Ni accumulated in the leaves. Therefore, the already known Ni-stimulated growth of O. bertolonii at increasing metal concentrations in the low-dose zone could be explained by a Ni-induced activity of urease, associable to an enhanced nitrogen metabolism, unless other still unknown physiological functions of Ni in hyperaccumulating plants.

APA, Harvard, Vancouver, ISO, and other styles

3

Souza, Thamy Lara. "Controles mineralógicos e geoquímicos do níquel não sulfetado em rochas ultramáficas no Escudo Sul-Riograndense." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2014. http://hdl.handle.net/10183/94678.

Full text

Abstract:

Este trabalho tem como objetivo investigar os processos controladores da mobilidade e concentração de níquel (Ni) em rochas ultramáficas serpentinizadas no Escudo Sul-Riograndense (ESrg), Rio Grande do Sul (RS), Brasil. A composição primária das rochas ultramáficas hospedeiras de Ni constitui um parâmetro relevante, mas os processos secundários são os controladores mais importantes dessas mineralizações, principalmente a serpentinização, pressupondo-se que o Ni possa migrar da olivina ou metamórfica para os minerais do grupo das serpentinas. Para a caracterização mineralógica e textural das rochas ultramáficas serpentinizadas da porção oeste do ESrg, foram aplicadas técnicas de petrografia e Microscopia Eletrônica de Varredura. Para a análise química dos elementos em rocha total foi realizada fluorescência de Raios-X, ICP e ICP-MS. Estas técnicas permitiram classificar quimicamente as rochas e relacionar a variação da intensidade dos eventos metassomáticos, metamórficos e hidrotermais que modificaram a mineralogia dos protólitos. No entanto, foram necessárias estudos de detalhe dos minerais individuais, notadamente olivinas e serpentinas com o uso da microssonda eletrônica para determinar as concentrações de Ni e suas variações nos diferentes corpos ultramáficos investigados. Dessa forma, foi possível quantificar e identificar os minerais concentradores de Ni e a relação dos eventos com a mobilidade e concentração dos elementos. Os resultados de microssonda indicam que as olivinas dos peridotitos do Maciço Pedras Pretas possuem baixos teores de níquel que variam de 0,13% a 0,21% e a média é 0,17%, enquanto que as olivinas dos harzburgitos da Sequência Cerro Mantiqueiras possuem teores mais elevados na média de 0,31%. As olivinas do Pedras Pretas possuem composição homogênea enquanto que aquelas do Cerro Mantiqueiras mostram variações composicionais importantes com conteúdo de Fo 92-98 e teores de níquel entre 0,3% e 0,4%. Tais variações no Cerro Mantiqueiras podem estar relacionadas a diferenças na composição do protólito ou a outro fator desconhecido que necessita futuras investigações. As olivinas e serpentinas no Cambaizinho e Serrinha mostram valores de níquel entre 0,19% a 0,3%, comparáveis ao Cerro Mantiqueiras, porém bem mais elevados que o Pedras Pretas. Este estudo mostra que os corpos ultramáficos do Cambaizinho- Serrinha e Cerro Mantiqueiras possuem potencial para desenvolver depósitos de Ni não sulfetado devido as concentrações relativamente elevadas de Ni nas olivinas. Entretanto, tais depósitos não se desenvolveram devido a dois fatores principais: o primeiro está ligado à superposição de eventos de metamorfismo e deformação recorrentes no tempo e no espaço que propiciaram a mobilização do Ni; o segundo fator é atribuído a ausência de agentes supergênicos favoráveis para a formação de depósitos lateríticos como os observados na região norte do Brasil. This paper investigates the processes controlling the mobility and concentration of nickel (Ni) in serpentinized ultramafic rocks in the Sul- Riograndense Shield (ESrg), Rio Grande do Sul (RS), Brazil. The primary composition of the ultramafic Ni host is a relevant parameter, but the secondary processes are the almost important controllers of these mineralizations, mainly serpentinization, assuming that Ni may migrate from igneous or metamorphic olivine minerals to the group of serpentine this phase. For the mineralogical and textural characterization of the serpentinized ultramafic rocks of the western portion of ESrg, were applied techniques of petrographic and scanning electron microscopy. For chemical analysis of elements in rock whole was performed X-ray fluorescence, ICP and ICP-MS. Although these techniques allow chemically classification of rocks and relate the variation of intensity in which metasomatics, metamorphic and hydrothermal events, changed the that mineralogy of the rock, however analysis of individual mineral detail, notably olivine and serpentine minerals using the electron microprobe detail, were necessary to determine the concentrations of Ni and variations in different ultramafic bodies investigated. Thus, it was possible to quantify and identify the Ni concentrators minerals and the relationship of events with the mobility and concentration of the elements. The microprobe results indicate that the olivine of peridotite Pedras Pretas have low contents of NiO ranging from 0.13% to 0.21% and averaged 0.17%, while the olivine harzburgites Cerro Mantiqueiras have higher levels of NiO averaging 0.31%. The olivine of Pedras Pretas have a homogeneous composition as those of Cerro Mantiqueiras show important compositional variations with a content of forsterite the Fo 92-98 and NiO contents of between 0.20% and 0.40%. Such variations in Cerro Mantiqueiras may be related to differences in the composition of the protolith or another unknown factor that needs further investigation. The olivine and serpentine in Cambaizinho and Serrinha, show NiO values between 0.19 % to 0.3 %, values comparable to the Cerro Mantiqueiras, but higher than the Pedras Pretas. This study shows that the Cambaizinho, Serrinha and Cerro Mantiqueiras have the potential to develop non- sulphide Ni deposits, due high Ni concentrations in olivine. However, these deposits are not developed due two main factors: the first is linked to the superposition of events the metamorphism and deformation applicants in time and space, that enabled the Ni mobilization; the second factor is attributed to lack preservation of profiles suitable for the Ni concentration, due to uplift and erosion lateritic subsequent.

APA, Harvard, Vancouver, ISO, and other styles

4

Scoon, Roger N. "Discordant bodies of postcumulis, ultramafic rock in the upper critical zone of the Bushveld complex : iron-rich ultramafic pegmatite bodies at Amandelbult and the Driekop platiniferous ultramafic pipe." Thesis, Rhodes University, 1986. http://hdl.handle.net/10962/d1004912.

Full text

Abstract:

From the abstract: In the layered sequence of the Bushveld Complex a number of distinct, but possibly genetically related groups of transgressive, postcumulus, ultramafic and mafic rock are recognised. The main part of this thesis investigates a suite of postcumulus rocks for which the name iron-rich ultramafic pegmatite is proposed. The majority of iron-rich ultramafic pegmatite bodies examined are from the upper critical zone of the layered sequence at Rustenburg Platinum Mines Amandelbult Section, in the northern sector of the western Bushveld Complex. Field relationships imply that the iron-rich ultramafic pegmatites should be considered as an integral feature of the layered sequence, even though they transgress the cumulates. Consequently, this thesis also includes a study of the cumulate sequence at Amandelbult. A second group of postcumulus, ultramafic rocks which is investigated comprises latiniferous ultramafic pipes; the Driekop pipe has been selected as a case study. This thesis is presented in four sections, namely, an introduction and verview, and studies on the Driekop pipe, the cumulate sequence at mandelbult and the iron-rich ultramafic pegmatite suite. A new classification scheme of discordant bodies of postcumulus, ultramafic rock in he Bushveld Complex is proposed (see also Viljoen & Scoon, in press). In he scheme presented here, two main varieties of postcumulus, ultramafic rock re recognised, namely, non-platiniferous magnesian dunites and iron-rich ltramafic pegmatites.

APA, Harvard, Vancouver, ISO, and other styles

5

Remus, Marcus Vinicius Dorneles. "Geologia e geoquimica do complexo cambaizinho, sao gabriel - RS." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 1990. http://hdl.handle.net/10183/5238.

Full text

Abstract:

Mapeamentos geológicos feitos pelo autor na região do Arroio Cambaizinho - são Gabriel/RS, resultaram na definição do Complexo Cambaizinho, representado pelas seqüências meta-sedimentar e máfica-ultramáfica, intimamente associadas ao longo de toda a extensão da associação supracrustal. A seqüência meta-se dimentar é constitu1da por gnaisses quartzo-feldspáticos dominan tes, anfibolitos bandados e quartzitos subordinados, derivados de sedimentos areno-pelítico-carbonatados estruturados, de forma ritmica em ambiente subaquoso. Niveis composicionais de ocorrência restrita contendo estaurolita, definem o grau metamórfico (médio) para esta região. Intercalações de serpentinitos, xistos magnesianos variados e anfibolitos a granulação fina, na forma de camadas e/ou lentes interestratificadas nos meta-sedimentos indicam suas derivações a partir de derrames e/ou intrusões , ígneas de pequena profundidade de composição básica-ultrabásica. Este juntamente com níveis de sedimentos qu1micos intercalados e corpos de gabros, constituem a seqüência máfica-ultramáfica. O complexo, representa o segmento norte de um cintu rão supracrustal polideformado de forma geométrica aproximadamente linear, com orientação NNE, que se extende desde a localidade de Passo do Ivo, situado mais a sul, até a região objeto deste trabalho. Quatro fases de deformação dúcteis foram das para a área, estando as duas primeiras (Dl e D2) identifica associadas xx aos eventos metamórficos regionais Ml e M2. O metamorfismo mais antigo (Ml), assinalado por paragêneses diagnósticas em metapelitos alcançou o fácies anfibolito (zona da estaurolita), estando representado em outras litologias pela ocorrência de olivina metamórfica em paragênese com tremolita e/ou talco (meta-serpentinitos) e hornblenda mais oligoclásio/andesina em meta-básicas. O M2, mais jovem, atingiu o fácies xistos verdes, cujas assembléias mineralógicas se associam à foliação S2, de distribuição ir regular ao longo do cinturão. As condições fisicas de Ml foram de média P/T, similares às do metamorfismo Dalradiano. Intrusões graniticas na forma de lâminas (corpos ta bulares) durante a segunda fase de deformação D2, datados pelo mé todo Rb/Sr em 661 :: 29 Ma e agrupados sob a denominação de Granatóides Sanga do Jobim, fornecem idades mínimas para o complexo. Os vários grupos composiciconais da seqüência máfic~ -ultramáfica, individualizados com base em critérios petrográf~ cos e conteúdo de elementos maiores correspondem a: serpentinitos e olivina-talco ultramafitos (cumulados komatilticos); xis tos magnesianos à talco e clorita e anfibólio xistos (komatiitos); clorita-hornblenda xistos (basaltos komatiiticos), litos e metagabros (basaltos e gabros tolelticos). anfibo Estes vários tipos litológicos foram originados através de diferentes graus de fusão parcial do manto como indicado pelo hiato composicional de MgO (11 à 17%) e os diferentes padrões de ETR existentes entre os anfibolitos/metagabros (toleitos) e os serpentinitos/xistos magnesianos (komatiltos).As variações composicionais no interior de cada grupo, foram controladas pelo fracionamento (acumulação ou extração) de olivina e pouco ortopiroxênio (serpentinitos e olivina-talco ultramafitos)clinopiroxênios (clorita e anfibólios xistos, clorita hornblenda xistos), clinopiroxênio e plagioclásio (anfibolitos e metagabros). As abundâncias e os padrões de ERTL (elementos terras raras leves) enriquecidos, juntamente com os baixos valores das razões A1203/Ti02 e CaO/Ti02 das amostras de xistos magnesiinos das camadas A e B sugerem derivações deste material a partir de baixas percentagens de fusão de um manto enriquecido em mentos incompatíveis. As anomalias negativas de Ce e Eu na ele maio ria das rochas da seqüência máfica-ultramáfica indicam que protólitos ígneossofreram alterações em ambiente submarino. Geologic mapping performed by the author on the Camb~ izinho area resulted in the separation of the Cambaizinho Complexo This includes sedimentary and mafic-ultramafic metamorphosed se quences which area closely intertongued all over the supracrustal association. Meta sedimentary sequence is built up mainly by quartz- feldspáthic gneisses and less abundant banded amphibolites with minor amounts of quartzites. These supposedely represent metamorphosed subaqueous rithmically banded arenaceous marly sediments. At some levels of restrict occurrence, representing an iron rich composition, staurolite bearing metamorphic assemblages suggests medium grade of metamorphism for this region. Interfingered serpentinites, some varieties of magnesian schists and fine grained amphibolites enclosed in the meta sedimentary rocks suggests lava flows and low depth intrusions of basics/ultrabasic composition. These volcanic magmatic rocks altogether with gabro bodies and interlayered chemical sediments built up the mafic-ultramafic sequence. Cambaizinho Complex represents the northern segment of a supracrustal, multideformed, linear belt trending NNE which stretches from this area till Passo do Ivo to the south. Four deformation phases were recognized for this area being first and second(Dl and D2) associated to regional metamorphic events, Ml and M2. The oldest metamorphic episode (Ml) signaled by diagnostic paragenesis in metapelites reached amphibolite facies (staurolite zone) being represented in magnesian rocks by olivine-tremoliteItalc (meta-serpentinites) and hornblende-oligoclase/ andesine in metabasites. M2 metamorphic event, younger is represented by greenschist facies whose mineralogic assemblages are associated to S2 foliation irregularly distributed along the belt. Physical conditions for Ml metamorphism of intermediate values for P/T are comparable to those of Dalradian metamorphism. Granitic intrusions form sheaf-like bodies belong to the second phase of deformation (D2) give the minimum Rb/Sr age of 661 z29 Ma for the whole complex and were named Sanga do Jobim Gra nitoids. The whole compositional range of the mafic-ultramafic sequence separated on the petrographic cri teria and major elements contents are named serpentinites and olivine-talc ultramaphites (komatiitic cumulates), magnesian talc schists and chlorite-amphibole schists (komatiites), chlorite-hornblende schists (basaltic komatiites) and amphibolites and meta-gabros (tholeitic and gabros). The lithologic types above are thought to have originated by different degrees of partial mantle fusion as suggested by MgO hiatus (11-17%) and various ETR patterns found for amphibQ lites and meta-gabros(tholeites) and serpentinites/magnesian sch! sts (komatiites). Compositional variations in each group were cog troled by fractionation (accumulation/extraction) of olivine and minor orthopyroxene (serpentinites and olivine-talc ultramaphites) pyroxenes and lesser amounts of olivine (talc magnesian schists), clinopyroxenes (chlorite and amphibole schists and chlorite-hornblende schists), clinopyroxene and plagioclase (amphibolites and meta-gabros) . Abundancies and enriched patterns of LREE with low values of Al2Oa/Ti02 and CaO/Ti02 rates of altogether magnesian schists of A & B layers suggests derivations of this material from feeble percentages of fusion of the mantle enriched in incompatible elements. Negative Ce and Eu anomalies in most rocks of th~ mafic-ultramafic sequence point to protolites submited to altera tion in submarine environment.

APA, Harvard, Vancouver, ISO, and other styles

6

Georgiou, Elena. "Geologie, petrologie et petrochimie du complexe plutonique de la foret d'akapnou, chypre, et des gites de chromite associes." Orléans, 1987. http://www.theses.fr/1987ORLE2033.

Full text

Abstract:

L'etude cartographique en depit d'un tectonique complexe, a permis d'observer de bas en haut: sequence mantelique (harzburgites a enclaves dunitiques); sequence cumulative (dunite principale, plastiquement deformee, wchrlites, pyroxenites, gabbros et plangiogranites)

APA, Harvard, Vancouver, ISO, and other styles

7

Moffat, David Thomas. "The serpentinized ultramafites of the Shetland Caledonides." Thesis, University of Liverpool, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.328460.

Full text

APA, Harvard, Vancouver, ISO, and other styles

8

Boulet, Frederic. "Mycorrhizal symbiosis as a strategy for survival in ultramafic soils." University of Western Australia. Soil Science and Plant Nutrition Discipline Group, 2003. http://theses.library.uwa.edu.au/adt-WU2004.0051.

Full text

Abstract:

Ultramafic soils enriched in nickel, such as found in Australia and New Caledonia, are associated with unique, diverse and poorly known vegetation communities. Re-establishment of these highly specific ecosystems is still a challenge for Ni mining companies. Ultramafic vegetation communities are the outcome of a long evolution process resulting in their adaptation to the extreme soil conditions found on ultramafic outcrops. Mycorrhizal fungi, a very common plant symbiont, are generally thought to be beneficial to plants in other ecosystems, providing plants with phosphorus and even promoting metal tolerance in plants in some cases. We examined the hypothesis that mycorrhizal fungi may contribute to the survival of plants in ultramafic soil conditions. Bandalup Hill, an ultramafic outcrop enriched in Ni (South West of Western Australia) was selected to assess the contribution of mycorrhizal fungi to ultramafic plants. Soil constraints, in particular the degree of Ni toxicity, were assessed at two sites with ultramafic soils within the outcrop. Total metal, nutrient, DTPA extractable Ni and available P were measured in soil while Ni, Ca and Mg were tested in the soil solution. In addition, nutrients and metals were analyzed in shoots of some plant species occurring at each site: Eucalyptus flocktoniae, Melaleuca pomphostoma, Melaleuca coronicarpa and Hakea verucosa. Topsoils in Bandalup Hill and plant shoots had high levels of Ni, and very low levels of P, K and N. Variation in DTPA extractable Ni between sites reflected the variation in shoot Ni level of E. flocktoniae and M. pomphostoma. Variations in soil solution Ni levels reflected variations in shoot Ni levels of M. coronicarpa and H. verucosa between sites. The germination requirements of the plant species used to assess the soil constraints was assessed. Species selected included Eucalyptus flocktoniae, Melaleuca coronicarpa, and Hakea verucosa. Seeds of E. flocktoniae and M. coronicarpa had a higher germination rate if pre-treated with smoke water, while no pre-treatment was required to germinate H. verucosa seeds. The unusual germination requirement of E. flocktoniae and M. coronicarpa involve complex chemical signals that may be present in the soil when the conditions are more favorable for plant establishment. Such unusual germination requirement may represent an adaptation to the hostile conditions of the ultramafic soils of Bandalup Hill. The mycorrhizal association and root characteristics of the selected plant species was also assessed after 8 weeks of growth in undisturbed ultramafic topsoil cores from Bandalup Hill. Roots of these species (including H. verucosa from a previously designated non-mycorrhizal family, Proteaceae) were associated with mycorrhizal fungi. Roots of E. flocktoniae and M. coronicarpa were colonized by both arbuscular mycorrhizal fungi (AMF) and ectomycorrhizal fungi (ECM), while roots of H. verucosa only contained some AM fungal structures. All species had high shoot to root ratios and their root characteristics reflected their association with mycorrhizal fungi. Based on the previous observations, uninoculated and inoculated E. flocktoniae seedlings were grown for 10 to 16 weeks in sand amended with Ni at 0, 0.2, 1 and 2.3 mg/kg. Mycorrhizal inoculum consisted of spores of Pisolithus sp. (ECM) or a mix of AMF spores and colonized root fragments, both originating from Bandalup Hill. Another inoculum consisted in Pisolithus sp. spores from a site with ultramafic soils in New Caledonia. Inoculation with AM and ECM fungi from Bandalup Hill was beneficial to E. flocktoniae. Benefits consisted mainly of a reduction of Ni shoot translocation at the highest Ni soil level. At 1 mg/kg soil Ni, E. flocktoniae exhibited a certain degree of tolerance to Ni. A substantial increase in growth and nutrient uptake with Pisolithus sp. from Western Australia was also observed. The contribution of AM fungi from Bandalup Hill to E. flocktoniae, M. coronicarpa, H. verucosa, and Trifolium subterraneum (clover) was then examined in ultramafic soil from Bandalup Hill.Steaming of ultramafic soil increased the availability and plant uptake of P. Consequently, uninoculated seedlings grew better, and inoculation with AM fungi decreased the growth of native plant species but did not affect their shoot Ni concentration. The presence of AM fungi increased the concentration of P in shoots of native plants species. Inoculation had no effect on the growth and nutrient content of subterranean clover. As mining activities have the potential to reduce the infectivity of AM fungi in topsoils, the effect of disturbance and storage practices on the AM infectivity of ultramafic topsoils collected in summer or winter from Bandalup Hill was investigated. Disturbance consisted in passing topsoil through a 2mm seive and cutting roots into 1cm fragments. Disturbed topsoil was then stored at room temperature in pots that were either sealed from the atmosphere or left open, and pots were maintained at field capacity. E. flocktoniae seedlings were planted in undisturbed and disturbed topsoil just after topsoil collect and then after 3, 6 and 9 months of topsoil storage. AM fungi present in the topsoil collected in summer was less susceptible to initial disturbance than AM fungi present in topsoil collected during winter. Also, storage of topsoil in sealed pots watered to field capacity was more detrimental to its infectivity than storage of topsoil in dry conditions. Mycorrhizal fungi can contribute to the survival of some native plant species in the ultramafic soils of Bandalup Hill and they may represent another strategy to improve the success of Ni mine revegetation. However, such contribution may not be the unique avenue for native plants to survive in ultramafic soils of Bandalup Hill.

APA, Harvard, Vancouver, ISO, and other styles

9

Uddin, Salah. "Surface charge characterization and flotation of an ultramafic nickel ore." Thesis, McGill University, 2012. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=107688.

Full text

Abstract:

AbstractAbout 300 million tonnes of inferred Ni resource in ultramafic hosted rocks is present in 'Thompson Nickel Belt' in north central Manitoba. The processing challenges result from electrostatic interaction between pentlandite (the main Ni-mineral) and serpentine (the main gangue and one of the MgO minerals). As a contribution to meeting the challenge, the thesis examines the role of particle and bubble surface charge and the effect of fibre disintegration on flotation behavior of an ultramafic Ni ore sample. For surface charge characterization the sedimentation potential technique was used. A novel integrated device was developed to measure sedimentation potential, conductivity and pH simultaneously. Maxwell's model was used to calculate volume fraction of dispersed phase from conductivity, and zeta potential, when appropriate, was calculated from the Smoluchowski equation. The technique was validated by showing good agreement with iso-electric point for alumina, silica and bubble suspensions with electrophoresis measurements. The technique was extended to characterize mixed minerals including ultramafic ore, and bubbles in the presence of particles. The results provided some evidence of metal ion adsorption on particles and the possibility of non-hydrophobic particle attachment to bubbles. The latter was reinforced by visualization studies of a pendant bubble exposed to particle suspensions.A novel fibre disintegration strategy was devised combining both chemical (acid) and physical (grinding) treatment based on work to enhance carbon dioxide uptake by serpentine. Using HCl, subsequent conventional flotation (amyl xanthate, soda ash and MIBC) gave significantly improved results over the untreated ore. Using H2SO4, arguably the practical option led to flotation without collector due to elemental sulphur formation on pentlandite, and without frother due to high ionic strength solutions. Improved Ni grade-recovery with higher MgO mineral rejection was achieved. Structural changes in the fibres were followed using various spectroscopic techniques and a mechanism of fibre disintegration suggested. Environ 300 millions de tonnes de ressources inférées de Ni ultramafiques hébergé est présent dans 'ceinture nickélifère de Thompson' dans le centre-nord du Manitoba. Le traitement des défis résultant de l'interaction électrostatique entre pentlandite (le principal Ni-minéraux) et la serpentine. En tant que contribution à relever le défi, la thèse examine le rôle des particules et la charge de surface des bulles et l'effet de la désintégration des fibres sur le comportement de flottaison d'un échantillon de minerai de nickel ultramafiques. Pour la caractérisation de charge de surface de la technique de sédimentation potentielle a été utilisée. Un nouveau dispositif intégré a été développé pour mesurer le potentiel de sédimentation, la conductivité et le pH simultanément. Le modèle de Maxwell a été utilisée pour calculer la fraction volumique de phase dispersée de la conductivité, et le potentiel zêta, le cas échéant, a été calculée à partir de l'équation de Smoluchowski. La technique a été validée en montrant un bon accord avec l'iso-électrique de point pour les suspensions d'alumine, de silice et de bulles avec des mesures d'électrophorèse. La technique a été étendue afin de caractériser les minéraux mélangés, y compris de minerai ultramafiques, et des bulles dans la présence de particules. Les résultats ont fourni des preuves de ion métallique adsorption sur les particules et la possibilité de l'attachement des particules non-hydrophobe à bulles. Ce dernier a été renforcée par des études de la visualisation d'une bulle Pendentif exposés à des suspensions de particules.Une stratégie nouvelle fibre de désintégration a été conçu combinant à la fois chimique (acide) et physiques (broyage) un traitement basé sur le travail pour améliorer l'absorption du dioxyde de carbone par la serpentine. En utilisant HCl, à la suite de flottation conventionnelle (amyl xanthate, la cendre de soude et de MIBC) a donné des résultats nettement améliorés au cours des minerais non traités. Utiliser H2SO4, sans doute l'option la pratique conduit à de flottaison sans collecteur due à la formation du soufre élémentaire sur la pentlandite, et sans buse due à des solutions à haute force ionique. Amélioration de qualité Ni-reprise avec le rejet supérieur de MgO de a été atteint. Les changements structurels dans les fibres ont été suivis en utilisant diverses techniques de spectroscopie et d'un mécanisme de désintégration de fibre suggéré.

APA, Harvard, Vancouver, ISO, and other styles

10

Phillips, David. "Mineralogy and petrology of the Townlands iron-rich ultramafic pegmatite." Thesis, Rhodes University, 1985. http://hdl.handle.net/10962/d1007617.

Full text

Abstract:

The Townlands iron-rich ultramafic pegmatite is a relatively large pipelike body situated in the western corner of Rustenburg Section, Rustenburg Platinum Mines. It is characterised by a strong negative magnetic signature and transgresses the noritic layered sequence of the upper critical zone of the Bushveld Complex. The layered rocks are downwarped in the vicinity of the pipe and are in sharp contact with the pegmatitic material. The pegmatite varies in composition between dunite and wehrlite, with the marginal zones being more wehrlitic in composition. Olivine (Fo₃₀ - Fo₅₂) and clinopyroxene (Wo₄₅En₃₀Fs₂₅ - Wo₄₅En₃₇Fs₁₈) are the dominant constituents and accessory phases include ilmenite, Ti -magnetite, apatite, amphiboles, chlorite-group minerals, biotite, ilvaite and a host of unusual ore minerals. The Fe-Ti oxides exhibit exsolution textures typically found in slowly cooled igneous rocks and temperatures of formati on are consi dered to be in excess of 800°C. The UG2 chromitite leader layers intersected by borehole TLP.l are enriched in Fe and Ti and exhibit compositions intermediate between chromite and Ti-magnetite. The ore mineral assemblage includes a primary sulphide assemblage consisting of troilite, chalcopyrite, cubanite and pentlandite, and an array of unusual phases formed by late-stage secondary processes. The unusual sulphides mooihoekite and haycockite, that occur in certain parts of the pegmatite, are considered to have formed by partial replacement of the primary assemblage and a possible paragenetic sequence is discussed. Mineral compositions and whole rock geochemical data are consistent with an origin for the pegmatite by crystallization from a fractionated melt. It is suggested that intercumulus fluids, trapped during the crystallization of the noritic layered sequence, accumulated in an area of structural weakness, in response to an increasing overburden pressure and/or tectonic activity. Evidence is also presented that indicates that the Townlands pegmatite may consist of at least two separate, but adjoining pegmatite bodies. KMBT_363 Adobe Acrobat 9.54 Paper Capture Plug-in

APA, Harvard, Vancouver, ISO, and other styles

11

Li, Jiajie. "Mechanical activation of ultramafic mine waste materials for enhanced mineral carbonation." Thesis, University of British Columbia, 2017. http://hdl.handle.net/2429/61039.

Full text

Abstract:

The potential success of integrating mineral carbonation, as a pathway to CO₂ sequestration, in mining projects, is dependent on the mineralogical composition and characteristics of its waste rock and tailings. Ultramafic rocks have proven the best potential substrate for mineral carbonation and their ability to alter and to convert CO₂ into its carbonate mineral form is dependent on the original mineralogy and particle surface area. CO₂ conversion kinetics is complex and with the application of appropriate comminution technologies, its efficiency can be enhanced. The objective of this research is to evaluate mechanical activation to enhance the carbonation storage capacity of mine waste material. Three approaches were taken in this research. The first approach was to characterize the microstructure of the mechanically-activated mineral olivine, a predominant mineral constituent of ultramafic rocks, using X-ray diffraction patterns and line profile analysis methods with full pattern fitting method. The second approach was to compare the structural and chemical changes of mine waste with pure olivine, both of which were activated by various mechanical forces under both wet or dry conditions and subsequently carbonated in a direct aqueous carbonation process. Regardless of milling conditions, forsterite (Mg₂SiO₄), the olivine mineral variety in the mine waste, was found to be the main mineral being mechanically-activated and carbonated. It was determined that lizardite (Mg₃(Si₂O₅)(OH)₄), a hydrated magnesium silicate also common in ultramafic hosted mineral deposits, acted as catalyzer assisting forsterite reaching high levels of activation. This condition generated a greater CO₂ conversion to carbonate than that of pure olivine with the equal specific milling energy input. The stirred mill proved to be the most efficient form of mechanical activation vis-a-vis the direct aqueous carbonation process, followed by the planetary mill and the vibratory mill. The third approach analyzes the feasibility of mechanical activation in an integrated mineral carbonation process in a nickel mine considering the life cycle of the process. The minimum operating cost for 60% CO₂ sequestration efficiency was 105-107 $/t CO₂ avoided. At this point, the Turnagain project can potentially sequester 238 Mt/y CO₂ using its waste during the 28-year life of mine. Applied Science, Faculty of Mining Engineering, Keevil Institute of Graduate

APA, Harvard, Vancouver, ISO, and other styles

12

de, Oliveira Elson Paiva. "Petrogenesis of mafic-ultramafic rocks from the Precambrian Curaca terrane, Brazil." Thesis, University of Leicester, 1990. http://hdl.handle.net/2381/35079.

Full text

Abstract:

The Caraiba copper-rich hypersthenite-norite complex in the Early Proterozoic Curaca terrane of northern Bahia, Brazil, is not a tholeiitic layered sill as has been previously suggested. It is re-interpreted as a series of multiple dyke-like intrusions, possibly derived through partial melting of an incompatible element enriched harzburgitic to orthopyroxenitic lithospheric mantle source region. It contains peridotitic and gabbroic xenoliths. Copper-rich gabbroic xenoliths may represent volcanic rocks taken to upper mantle depths by a process of subduction. The chemistry of some of the regional mafic rocks and of three granitoid generations suggest for the Curaca terrane a tectonic evolution similar to Phanerozoic continent-continent collision belts, which was possibly initiated at an Andean-type margin. A Middle Proterozoic mafic dyke swarm that post-dates the main period of crustal growth is interpreted as having originated from a heterogeneous garnet-bearing source in the asthenospheric mantle, and is likely to be related to a mantle plume or hotspot during the development of the coeval Espinhaco aulacogen. The parental magma of these dykes is thought to have resided in small zoned magma chambers. Comparison with other mafic dykes from the Brazilian shield suggests derivation of the Early Proterozoic dykes from more depleted, more refractory, lithospheric mantle sources than those of the younger dykes, which are believed to have had a significant asthenospheric contribution in their petrogenesis. The chemistry of these dykes reflects the evolution of the sub-continental mantle with time.

APA, Harvard, Vancouver, ISO, and other styles

13

Layton-Matthews, Daniel. "Metasomatism of ultramafic intrusions in the Thompson Nickel Belt, Manitoba, Canada." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp05/mq61276.pdf.

Full text

APA, Harvard, Vancouver, ISO, and other styles

14

Khan, Mohammad Asif. "Petrology and structure of the Chilas ultramafic complex, NW Himalayas, Pakistan." Thesis, Imperial College London, 1989. http://hdl.handle.net/10044/1/47506.

Full text

APA, Harvard, Vancouver, ISO, and other styles

15

Entezari, Zarandi Ali. "Dynamics of passive minerals carbonation in ultramafic mining wastes and tailings." Doctoral thesis, Université Laval, 2017. http://hdl.handle.net/20.500.11794/27833.

Full text

Abstract:

L'élaboration de stratégies économiquement viables pour le stockage à long terme du dioxyde de carbone est devenue depuis quelques années un enjeu majeur en réponse aux préoccupations liées au réchauffement planétaire. Le captage et stockage du carbone (CSC) est considéré comme l'un des scénarios possibles visant à contrer le phénomène du réchauffement planétaire en ciblant le CO₂ atmosphérique. La carbonatation minérale – dans des plateformes de CCS – devrait être une option privilégiée pour la capture et le stockage permanent du carbone, connaissant la réactivité de matériaux alcalins tels que les silicates de magnésium et la brucite avec le dioxyde de carbone pour former des carbonates stables et respectueux de l'environnement. La carbonatation minérale passive des minéraux contenus dans les rejets ultramafiques pourrait être considérée comme une option économiquement attrayante en raison de la disponibilité de grandes quantités de rejets miniers riches en magnésium, de granulométrie très fine et hautement réactifs. De plus, les réactions impliquées dans la carbonatation minérale se font relativement facilement dans les conditions ambiantes. Le CO₂ est principalement dissous dans l'eau provenant de la pluie et de la fonte des neiges pour former des ions HCO₃₋ et CO₃²⁻. Des ions métalliques tels que le Mg²⁺ et le Ca²⁺ sont également lessivés dans l'eau permettant ainsi la formation de carbonates métalliques. Des travaux expérimentaux de laboratoire ont été réalisés afin d'identifier la dynamique de la carbonatation minérale passive dans des conditions environnementales qui prévalent généralement dans les régions du Québec, au Canada. Une cellule de carbonatation à diffusion différentielle a été développée pour suivre la cinétique de carbonatation minérale dans des conditions ambiantes. Les mesures cinétiques ont révélé le rôle complexe de l'eau à la fois dans le milieu réactionnel et en partie dans les processus de carbonatation. L'analyse par diffraction aux rayons X en fonction du temps et les observations au microscope électronique à balayage révèlent la formation de carbonates de magnésium intermédiaires, poreux et métastables qui ont ensuite évolué en couches de nesquehonite moins poreuses. Ces minéraux secondaires sont responsables de la passivation des surfaces malgré la disponibilité d’une partie de la brucite qui n’avait pas encore réagie. Cependant, les résultats ont montré que l'abrasion des surfaces de rejets préalablement carbonatés peut permettre l’exposition de surfaces fraiches permettant ainsi une carbonatation supplémentaire des résidus. Des essais de carbonatation à température variable ont été effectués dans les plages de température chaude (35 ± 1 ° C), de laboratoire (23 ± 2 ° C), faible (5 ± 1 ° C) et de congélation (-5 ± 2 ° C) pour considérer les différences saisonnières. Les résultats suggèrent que la température a un effet notable sur la cinétique de carbonatation et une baisse de la température a provoqué un ralentissement de la réaction, bien que la carbonatation soit, d’un point de vue thermodynamique, définie comme une réaction exothermique. De plus, il a été observé que le séchage et les cycles de gel/ dégel étaient à l'origine d'un effet thermomécanique de "pelage" qui induit des microfractuations des couches de carbonates secondaires permettant à l'eau et au gaz de migrer et de réagir avec des sites donneurs de Mg. L'analyse par spectroscopie FTIR a révélé que des carbonates de magnésium hydratés tels que la nesquehonite se forment parallèlement à la dissolution de la brucite pendant la carbonatation minérale des résidus miniers de nickel riches en brucite. Cependant, les résultats suggèrent aussi que la nesquehonite n'est pas le produit final de carbonate de magnésium hydraté. En effet, une surveillance à long terme (sur 2 ans) d'un matériau déjà carbonaté a révélé que la nesquehonite initiale a évolué en dypingite et en hydromagnésite, dépendamment de l'âge, des cycles de mouillage/séchage et de la profondeur où le carbonate initial s'est formé. Néanmoins, la nesquehonite pourrait maintenir sa stabilité sur des périodes prolongées si elle n'est pas soumise à des conditions humides. Developing economically feasible strategies for long-term storage of carbon dioxide has become over the past few years a major stake in response to the concerns over global warming. Carbon capture and storage (CCS) is widely believed to be one of the possible scenarios aimed in challenging the global warming phenomenon by targeting the atmospheric CO₂ content. Mineral carbonation – in the platform of CCS – is anticipated to be a premium option for permanent carbon capture and storage owing to the known reactivity of alkaline materials such as magnesium silicates and brucite with carbon dioxide to form stable and environmentally benign carbonates. Passive mineral carbonation of ultramafic mine waste and tailing minerals could be considered as an economically attractive option owing the availability of large amounts of magnesium-rich mining wastes, which are regarded to be virtually free, typically fine grained and highly reactive. Moreover, the energy input of nature is employed in passive mineral carbonation which is likewise free. In this way, CO₂ is mainly dissolved in water resulting from rain and snow season. Metal ions such as Mg²⁺ and Ca⁺ are also leached into the water allowing the formation of metal bicarbonate and consequently formation of metal carbonates. Laboratory experimental works were done in order to identify the dynamics of passive mineral carbonation under environmental conditions prevailing the Quebec region, Canada. A differential diffusion carbonation cell was developed to monitor the kinetics of mineral carbonation under ambient conditions. The kinetic measurements revealed the complex role of water both as reacting medium and moiety in the carbonation pathway. Time-dependent X-ray powder diffraction analysis and scanning electron microscopy reveal formation of transitional, metastable porous, flaky magnesium carbonates which subsequently evolved into less porous nesquehonite layers, which are shown to be responsible for surface passivation despite availability of unreacted brucite. However, surface abrasion was shown to liberate previously carbonated NIMT particles resulting in further carbonation on freshly exposed surfaces. Temperature dependent carbonation tests were performed in the ranges of hot (35 ± 1 °C), laboratory (23 ± 2 °C), low (5 ± 1 °C), and freezing (-5 ± 2 °C) to mimic different seasonal conditions. Temperature had a notable effect on the carbonation kinetics and lowering temperature caused a reaction slowdown despite carbonation is thermodynamically defined as an exothermic reaction. Moreover, it was observed that drying and freeze/thaw cycles were at the origin of a thermomechanical “peel-off” effect which inflicted micro–fractures to the carbonate product layers enabling water and gas to engulf beneath and react with freshly unearthed Mg donor sites. FTIR spectroscopy analysis revealed that hydrated magnesium carbonates such as nesquehonite are being formed parallel to brucite dissolution during mineral carbonation of brucite-rich nickel mining tailings. However, it was observed that nesquehonite is not the ultimate hydrated magnesium carbonate product. Long–term monitoring over 2 years of an already carbonated material revealed that the initial nesquehonite has evolved into dypingite and hydromagnesite depending on age, wetting/drying history and the depth where initial carbonate has been formed. Nonetheless, nesquehonite could maintain its stability over prolonged times if not being subjected to wet/ humid environmental conditions.

APA, Harvard, Vancouver, ISO, and other styles

16

Leung, Ho-sun. "Geochemistry of the paleozoic Xiadong mafic-ultramafic complex, Eastern Xinjiang, NW China." Click to view the E-thesis via HKUTO, 2010. http://sunzi.lib.hku.hk/hkuto/record/B44143850.

Full text

APA, Harvard, Vancouver, ISO, and other styles

17

Kieser, Nigel Bernard John. "Platinum-group element dispersion associated with mafic and ultramafic rocks in Alaska." Thesis, Imperial College London, 1996. http://hdl.handle.net/10044/1/8235.

Full text

APA, Harvard, Vancouver, ISO, and other styles

18

Leung, Ho-sun, and 梁灝燊. "Geochemistry of the paleozoic Xiadong mafic-ultramafic complex, Eastern Xinjiang, NW China." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2010. http://hub.hku.hk/bib/B44143850.

Full text

APA, Harvard, Vancouver, ISO, and other styles

19

Nagy, Laszlo. "Ecological investigations on selected species at the Meikle Kilrannoch Ultramafic Outcrops, Scotland." Thesis, University of Stirling, 1994. http://hdl.handle.net/1893/11843.

Full text

Abstract:

Ecological and ecophysiological investigations carried out at the ultramafic outcrop near Meikle Kilrannoch, Angus, Scotland are reported. The outcrop is botanically famous for its rare plant species, particularly the endemic Cerastium fontanum ssp. scoticum and the nationally rare Lychnis alnina. The studies were made on the main outcrop (called MK1) which is dome shaped, and on a much smaller low-lying area (called MK1.5) about 300 m from it. The overall aim of the studies was to investigate the relationship between the soil physico-chemical environment and species distribution on the open areas of the ultramafic site and to experimentally test for causality; and to offer an explanation for the open character of the vegetation on the skeletal soils. Variograms which were constructed for soil properties and vegetation data to investigate soil micro-spatial variation and vegetation pattern showed differing levels of spatial dependence, always indicating high intrinsic variability. The cause of this high variability was probably cryoturbation for the soil and morphological characters for plants. The gradient analyses (Principal Components Analysis and its canonical form, Redundancy Analysis) used to study soil - vegetation correlations suggested that A ostis vinealis, Cerastium fontanum ssp. scoticum and Lychnis alpina were most abundant in areas up-slope with lower concentrations of soil magnesium; Cochlearia pyrenaica ssp. alpina and Festuca rubra were associated with bigger stone sizes, and the latter occurred in wetter areas with higher of ions. A comparative solution culture experiment based on the local soil chemistry was used to study the growth responses to magnesium and nickel of Cerastium fontanum ss. scoticum, Cochlearia pyrenaica ssp. al ina and Festuca rubra. The results for Festuca and Cerastium were in agreement with the findings of the gradient analysis: Festuca was indifferent to both magnesium and nickel and Cerastium was susceptible to high magnesium; the reduction of dry weight by nickel in the Cochlearia conflicted with its suggested association with high soil nickel in the gradient analysis. The impacts on the photosynthetic systems of three Cochlearia species of different concentrations of iron and nickel were identifiable only in the non-ultramafic C. pyrenaica where the addition of nickel decreased photosynthesis but the effect could be ameliorated by the addition of high concentrations of iron. The open character of the skeletal soil at the MK1 site was discussed in terms of 'carrying capacity'. Vegetation development was suggested to be controlled at least partly by large stones covering the soil surface. Further factors such as space fragmentation, possible plant-to-plant interactions, and low density of flowering individuals and restricted seed dispersal were also considered. To test if major nutrients were limiting plant growth, major nutrients (NPK) were applied to the MK1.5 skeletal soil. The significantly higher X's and recruitment and change in life history traits (larger rosette sizes, earlier maturing and higher seed production) in the fertilised populations of C. pyrenaica ssp. alpina resulted in a significantly higher plant cover in the fertilised quadrats. The better growth of plants in the fertilised quadrats was reflected in their lower total non-structural carbohydrate (TNC) concentrations in May and their higher TNC in August. The present series of investigations found that magnesium and nickel toxicity had an effect on the intra-site distribution of the ultramafic species and also confirmed earlier reports on the importance of magnesium and nickel toxicity in ultsamafic exclusion. Large stones and low soil phosphorus concentration are proposed as limiting factors for the development of closed vegetation on the skeletal soil areas of the sites.

APA, Harvard, Vancouver, ISO, and other styles

20

Power, Matthew R. "Models for the genesis of industrial minerals in mafic and ultramafic rocks." Thesis, University of Exeter, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.245925.

Full text

APA, Harvard, Vancouver, ISO, and other styles

21

Emblin, S. R. "The Reinfjord ultramafic complex, Seiland province : emplacement history and magma chamber model." Thesis, University of Bristol, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.355634.

Full text

APA, Harvard, Vancouver, ISO, and other styles

22

Stanley, Jessica R. "The lattice preferred orientation of olivine in Beni Bousera Ultramafic Massif, Morocco." Thesis, Massachusetts Institute of Technology, 2009. http://hdl.handle.net/1721.1/55168.

Full text

Abstract:

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2009. Cataloged from PDF version of thesis. Includes bibliographical references (p. 93-101). The roll of melt in deformation of the mantle is important for understanding mantle processes and evolution. The Beni Bousera Ultramafic Massif, northern Morocco, shows petrologic evidence that melt was an important part of its history. The massif, dominantly composed of spinel lherzolite with harzburgitic sections, has 10 to 100 meter scale zones which contain abundant pyroxenite dykes, dunite, harzburgite, and secondary lherzolite. These zones are interpreted as areas of focused melt percolation. Lattice preferred orientation (LPO) of olivine crystals from a sample transect across one of these zones was analyzed in comparison with LPO from the surrounding host lherzolite and harzburgite. The LPO from peridotites within the zone was slightly different from those outside the zone, and the LPO from the dunite analyzed was significantly different from the peridotites. Within the melt percolation zone, orientation of the olivine a-axis with respect to the mineral foliation indicates that strain increases towards the center of the zone and that shear sense changes across the zone. This suggests that focused melt flow can induce deformation in its host peridotite. by Jessica R. Stanley. S.M.

APA, Harvard, Vancouver, ISO, and other styles

23

Pesce, Kathryn A. "Petrology and geochemistry of pyroxenites in the Lanzo ultramafic massif, Northwestern Italy." Thesis, Massachusetts Institute of Technology, 2012. http://hdl.handle.net/1721.1/70781.

Full text

Abstract:

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2012. "February 2012." Cataloged from PDF version of thesis. Includes bibliographical references (p. 43-45). Combined field, microtextural, and geochemical observations are presented for pyroxenites in the Lanzo ultramafic massif in order to place chemical and petrological constraints both locally on the geologic history of the massif and more generally on the role of magmatic rifting and the rift-to-drift transition in ultraslow-spreading ridge environments. Two separate generations of pyroxenites have been distinguished. A young set of primitive Cr-diopside websterites of MORB affinity are related to melt infiltrations and melt-rock reactions during rifting and Jurassic exhumation, while a much older generation of websterites likely of subcontinental origin were inherited and pre-date continental rifting and exhumation of the massif. The regional compositional and textural variation observed in the latter group of pyroxenites is not due to primary heterogeneities but rather to differences in subsequent metamorphic histories. Pyroxenites from the northern domain experienced a colder exhumation history and physical isolation from the rest of the massif by means of a high temperature shear zone related to the rifting. These websterites preserve garnet pseudomorphs and elevated REE which are textural and geochemical evidence for the prior coexistence of clinopyroxene and garnet. The implications of this study are that the Lanzo massif was indeed subcontinental lithosphere prior its exhumation and existence as an Ocean Continent Transition Zone (OCTZ) and that high temperature shear zones do seem to serve as effective permeability barriers and melt-focusing zones in rifting systems. by Kathryn A. Pesce. S.M.

APA, Harvard, Vancouver, ISO, and other styles

24

Craven, John Anthony. "The petrogenesis of some ultramafic rocks from the Gardar Province, S.W. Greenland." Thesis, University of Edinburgh, 1985. http://hdl.handle.net/1842/12171.

Full text

APA, Harvard, Vancouver, ISO, and other styles

25

Ford, Frederick Dean Carleton University Dissertation Geology. "Petrology of the Flinton Creek ultramafic rocks, central metasedimentary belt, Grenville province." Ottawa, 1989.

Find full text

APA, Harvard, Vancouver, ISO, and other styles

26

BENOIT, VINCENT. "Etat d'equilibre de peridotites du manteau superieur : application au plateau du colorado." Paris 7, 1987. http://www.theses.fr/1987PA077186.

Full text

Abstract:

Deux nouvelles calibrations de methodes thermobarometriques a partir de donnees experimentales. La premiere basee sur la solubilite de diopside entre clinopyroxene et orthopyroxene. Elle prend en compte l'effet d'elements mineurs tels que na et fe. Ce thermobarometre, combine avec le thermometre base sur la solubilite de l'enstatite dans les deux pyroxenes fournit un bon outil pour tester l'etat d'equilibre des peridotites a spinelle. La deuxieme calibration est basee sur la solubilite du chrome dans la spinelle et le grenat coexistants

APA, Harvard, Vancouver, ISO, and other styles

27

Ben, Jamaa Néjib. "Les peridotites de bay-of-islands (terre neuve) et de cap ortegal (espagne) : approche petro-structurale." Paris 7, 1988. http://www.theses.fr/1988PA077010.

Full text

Abstract:

Une nouvelle approche petrologique pour definir l'evolution des roches ultramafiques des massifs ophiolitiques est etablie, par l'etude petrochimique d'une serie harzburgitique de cherzolitique situe a terre neuve et par l'etude structurale et petrologique des peridotites et websterites du complexe du cap ortegal (espagne). Ce travail sert de support pour definir la methodologie permettant de suivre l'evolution des parametres chimiques lors d'une fusion partielle

APA, Harvard, Vancouver, ISO, and other styles

28

Stern, Fabio G. "Geochemistry of the Ultramafic Rocks from the Bay of Island Ophiolitic Complex, Newfoundland." Thèse, Université d'Ottawa / University of Ottawa, 2013. http://hdl.handle.net/10393/24159.

Full text

Abstract:

The Bay of Islands Ophiolitic Complex (BOIC) is one of most well preserved and well-exposed ophiolites in the world. The BOIC consist of four massifs; these are the Table Mountain (TBL), North Arm Mountain (NAM), Blow-Me-Down Mountain (BMD) and Lewis Hills massifs. Proposed geological environments of the BOIC in Newfoundland are diverse; ranging from oceanic spreading ridge to supra-subduction setting. The BOIC has a complete ophiolite sequence as defined at the Penrose Conference (Anonymous, 1972) including ultramafic mantle rocks, ultramafic to gabbroic cumulate rocks, sheeted dikes, pillowed basaltic rocks and capping sedimentary rocks in structurally ascending order. We studied harzburgite and overlying massive dunite in the BOIC. Harzburgite is generally medium-grained, and contains olivine, orthopyroxene, Cr-spinel, clinopyroxene and rare sulfide minerals. Harzburgite is massive to strongly deformed, with local development of mylonitic shear zones. A foliation and lineation are defined by elongated and fragmented grains of orthopyroxene and Cr-spinel. Dikes, sills, veins, and irregularly-shaped bodies of dunite and pyroxenite are present throughout the harzburgite unit. Dunite is the predominant lithology of the Blow-Me-Down Mountain. It is typically fine- to medium-grained, massive, and contains minor Cr-spinel and rare sulfide minerals. Dunite contains olivine, Cr-spinel and minor pyroxenes in some samples. Olivine crystals are commonly partly replaced by serpentine along fractures and in outer rims. Bulk rock and mineral composition data suggest that harzburgites are mild to highly refractory mantle residues after partial melting. In contrast all dunite samples show a cumulate geochemical signature from a mafic melt that originated from highly refractory mantle peridotites. Our study suggest that the harzburgite in the BOIC originally formed as oceanic lithosphere at a slow spreading ridge, possibly in the vicinity of active arc systems, whereas the parental melt for dunites formed in subduction setting. The second part of this study measured trace element compositions for olivine, Cr-spinel and bulk rock of dunite. The measured bulk rock compositions are compared to those of calculated based on mineral chemistry and their abundance. This comparison suggests that the trapped melt fraction was negligible during the crystallization of the dunites. The calculated melt compositions for the dunites confirm that the melt formed in subduction setting.

APA, Harvard, Vancouver, ISO, and other styles

29

Delgado-Argote, Luis Alberto 1953. "Geologic and economic study of ultramafic complexes of the coast of Guerrero, Mexico." Thesis, The University of Arizona, 1986. http://hdl.handle.net/10150/558060.

Full text

APA, Harvard, Vancouver, ISO, and other styles

30

Frison, Jean-Yves. "Les peridotites du massif ophiolitique du vourinos (grece) : etude petro-structurale, mise en evidence d'une structure diapirique." Paris 7, 1987. http://www.theses.fr/1987PA077112.

Full text

Abstract:

L'etude petrographique des facies permet de scinder le vourinos en trois unites lithologiques. L'analyse des donnees structurales, texturales et petrologiques conduit a interpreter le vourinos en terme de diapirisme. Par ailleurs, la determination de la composition chimique des differentes phases minerales et des conditions thermobarometriques revelent que les peridotites ont subi une rehomogeneisation a basse temperature et sous l'effet de le percolation de phase fluide. On considere que le cortege ophiolitique du vourinos resulte d'une refusion locale d'un manteau oceanique deja appauvri, vraisemblablement a l'aplomb d'une zone de subduction

APA, Harvard, Vancouver, ISO, and other styles

31

Ratié, Gildas. "Fractionnement isotopique naturel et anthropique du nickel en contexte ultrabasique : le cas des massifs de Niquelândia et Barro Alto (Etat du Goiás, Brésil)." Thesis, Paris 11, 2015. http://www.theses.fr/2015PA112229/document.

Full text

Abstract:

La région Centre Ouest du Brésil possède des massifs ultrabasiques (UB) avec des manteaux latéritiques représentants des réserves et ainsi des ressources économiques importantes de Ni. Ces massifs nickélifères permettent d’étudier le cycle du Ni sous contraintes anthropiques par une approche pluridisciplinaire, associant caractérisations chimiques, mesures physiques de sa spéciation solide, et traçage isotopique des sources et des processus affectant le nickel. Cette thèse focalisée sur l’utilisation des isotopes du Ni comme traceur a eu pour but d’identifier la signature isotopique au sein de plusieurs compartiments en interactions les uns avec les autres (roche mère, saprolite, latérite, sol et plantes) et d’associer les fractionnements observés aux processus biogéochimiques. De plus, du fait de leurs ressources économiques, les massifs étudiés, Barro Alto et Niquelândia, subissent une pression anthropique importante, minière et métallurgique. Ainsi, ils offrent une opportunité unique d’étudier le fractionnement isotopique du nickel associé à son cycle anthropique, et voir s’il est possible d’identifier la contribution anthropique dans le cycle naturel du Ni par sa signature isotopique. Les résultats ont montré que l’altération de roches UB conduit à un fractionnement isotopique du Ni, se traduisant par une perte en isotopes lourds de la phase solide, soit un Δ⁶⁰Ni de - 0,47 ‰ entre la roche mère et le top-sol. Ce fractionnement semble associé au moins en partie à l’incorporation et à la sorption des isotopes légers du Ni sur les oxydes de Fe lors de la remobilisation du Ni au cours de l’altération. Cet enrichissement en isotopes légers du Ni dans la partie solide conduit à une composition isotopique en Ni plus lourde dans la phase dissoute (eaux du massifs : 0.50 ‰ < δ⁶⁰Ni < 0,70 ‰). La zone saprolitique présente une variation importante de signature isotopique allant pour δ⁶⁰Ni de -0,04 ‰ à 1,41 ‰. Pour les échantillons présentant une signature isotopique lourde, le Ni se trouve principalement au sein de la serpentine fortement substitué, quand les signatures plus légères sont en lien avec une proportion de Ni plus importante au sein de la goethite. Dans un système comme celui-ci avec un nombre important de phases porteuses de Ni, il est cependant très difficile d’établir un lien entre la spéciation solide et l’isotopie du Ni. Le rôle des plantes dans le cycle du Ni a été abordé en étudiant le fractionnement isotopique du Ni dans trois espèces de plantes hyperaccumulatrices de Ni et deux espèces de plantes tolérantes. Il existe un fractionnement isotopique lors du transfert de Ni de la tige vers la feuille, qui est systématiquement enrichie en isotopes lourds du Ni. Les feuilles sont les compartiments des plantes où les teneurs en Ni sont les plus importantes. L’enrichissement en isotopes lourds du Ni des feuilles par rapport aux sols (- 1,05 ± 0,03 ‰ < Δ⁶⁰Ni_sol-feuilles < - 0,06 ± 0,12 ‰) semble indiquer que la restitution et la décomposition de cette matière organique au niveau du sol s’accompagnera d’un apport en isotopes lourds du Ni dans le sol. L’activité pyrométallurgique entraîne un fractionnement isotopique lors du processus de fusion en conditions réductrices qui conduit à la formation des scories de réduction. Ces résidus présentent un enrichissement en isotopes lourds (δ⁶⁰Ni = 0,18 ± 0,05 ‰) par rapport au matériel entrant (δ⁶⁰Ni = 0,08 ± 0,08 ‰) et au produit final, le FeNi (δ⁶⁰Ni = 0,06 ± 0,02 ‰). Enfin, cette étude montre que l’utilisation des isotopes du Ni pour tracer le Ni « anthropique » et le distinguer du Ni naturel possède certaines limites en raison du faible fractionnement induit par les processus pyrométallurgiques aux regards de la grande variabilité des échantillons naturels au sein de la littérature (-1.03 ‰ < δ⁶⁰Ni < 2.50 ‰) The Centre region the West of Brazil possesses ultramafic massifs (UM) with coats lateritic representatives of the reserves and so the important economic resources of Ni. These nickelifere massifs allow to study the cycle of Ni under anthropological constraints by a multidisciplinary approach, associating chemical characterizations, physical measures, solid speciation, and the isotopic drawing of sources and the processes affecting the nickel. This work focused on the use of the isotopes of Ni as tracer aimed at identifying the isotopic signature within several compartments in interactions some with the others (source rock, saprolite, laterite, soil and plants) and to associate the fractionation observed in the biogeochemical processes. Furthermore, because of their economic resources, the studied massifs, Barro Alto and Niquelândia, undergo an important, mining and metallurgical anthropological pressure. So, they offer an opportunity to study the isotopic fractionation of the nickel associated with its anthropological cycle, and to see if it is possible to identify the anthropological contribution in the natural cycle of Ni by its isotopic signature. The results showed that the weathering of rocks UB leads to an isotopic fractionation of Ni, being translated by a loss in heavy isotopes of the solid phase with a Δ⁶⁰Ni of - 0,47 ‰ between the bedrock and the top-soil. This division seems associated at least partially with the incorporation and with the sorption of the light isotopes in iron oxides during the remobilization of Ni. This enrichment in light isotopes in the solid part leads to a heavier isotopic composition in the dissolved phase (waters of massifs: 0.50 ‰ < δ⁶⁰Ni < 0,70 ‰). The saprolitic zone presents an important variation of isotopic signature (δ⁶⁰Ni) from -0,04 ‰ to 1,41 ‰. For samples presenting a heavy isotopic signature, Ni is mainly within the serpentine strongly substituted, when the lighter signatures are in connection with a proportion of Ni more important within the goethite. In a system as this one with a significant number of Ni-bearing phases, it is however very difficult to establish a link between the solid speciation and the isotopic composition. The role of plants in the cycle of Ni was approached by studying the isotopic fractionation of Ni in three species of hyperaccumulating plants of Ni and two species of tolerant plants. There is an isotopic fractionation during the transfer of Ni between the stem and the leaf, which is systematically enriched in heavy isotopes of Ni. The leaves are the compartments of the plants where the Ni contents are the most important. The enrichment in heavy isotopes of Ni in leaves with regard to soils (- 1,05 ± 0,03 ‰ < Δ⁶⁰Ni_sol-feuilles < - 0,06 ± 0,12 ‰) seems to indicate that the return and the decomposition of this organic matter at soil level will come along with a contribution in heavy isotopes of Ni in the soil. The pyrometallurgical activity lead to an isotopic fractionation during the smelting process in reducing conditions which leads to the formaton of the reduction slag. These slags present an enrichment in heavy isotopes (δ⁶⁰Ni = 0,18 ± 0,05 ‰) compared with the feeding material (δ⁶⁰Ni = 0,08 ± 0,08 ‰) and the end product, the FeNi (δ⁶⁰Ni = 0,06 ± 0,02 ‰). Finally, this study shows that the use of the isotopes of Ni to decipher the Ni anthropogenic and natural is limited because of the low fractionation induced by the pyrometallurgical processes in the looks of the big variability of the natural samples within the literature (-1.03 ‰ < δ⁶⁰Ni < 2.50 ‰)

APA, Harvard, Vancouver, ISO, and other styles

32

Wilson, Kelly. "RARE EARTH ELEMENTS AT HICKS DOME, SOUTHERN ILLINOIS, THEIR MODE OF MINERALIZATION AND RELATIONSHIP WITH IGNEOUS INTRUSIONS." OpenSIUC, 2019. https://opensiuc.lib.siu.edu/theses/2581.

Full text

Abstract:

Rare earth elements (REE) are an increasingly important group of metals due to their role in the development of modern technologies. Despite being abundant within the Earth’s crust recoverable ores are uncommon, and their mineralization isn’t as well understood as other abundant ore types. In this work, the mineralization of REE occurring in outcrop samples at Hicks Dome, a cryptoexplosive feature that resides in the Wauboukigou Alnöite Province in southeastern Illinois, was studied to determine the mode of mineralization and the origin of the REE. Xenotime-(Y) was identified with a scanning electron microscope in an intrusive breccia and emplaced during or shortly after the uplift which created the oval doming of the Paleozoic section. Whole rock REE concentrations from ultramafic dikes at Hicks Dome closely match global averages of lamprophyres and carbonatites, with a steep La to Lu slope, and enrichment of light rare earth elements. Hicks Dome has unique characteristics relative to the other intrusions in the Province, such as elevated REE, Th, and doming. These traits indicate that the dome was more closely related to an intrusive body at depth that sourced heat, volatile gases, and a suite of rare elements. Based on these data, the REE mineralization and thorium associated with the siliceous breccia is directly related to the alkaline ultramafic intrusion at Hicks Dome. The volatile rich, hot fluids emanating from the ultramafic magma supplied REE and thorium were mixed with the regional fluids responsible for the IKFD.

APA, Harvard, Vancouver, ISO, and other styles

33

Rodrigues, Analuiza Costa Pereira. "Rochas metamorficas maficas e ultramaficas do Greenstone Belt Barbacena na região de Itutinga, MG." [s.n.], 2000. http://repositorio.unicamp.br/jspui/handle/REPOSIP/287148.

Full text

Abstract:

Orientador: Asit Choudhuri Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Geociencias Made available in DSpace on 2018-07-26T20:30:50Z (GMT). No. of bitstreams: 1 Rodrigues_AnaluizaCostaPereira_M.pdf: 6857377 bytes, checksum: 8c4f1729d898f2b452b4aef4809d48dd (MD5) Previous issue date: 2000 Resumo: Na região de ltutinga-Nazareno, sudeste do estado de Minas Gerais, borda sudeste do Cráton de São Francisco, afloram rochas metamórficas vulcânicas máficas e ultramáficas de sucessões vulcano-sedimentares estudadas petrográfica e quimicamente nesta pesquisa geológica. As sucessões vulcano-sedimentares são constituídas por metabasaltos, metakomatiítos, e rochas metassedimentares associadas, e são consideradas pertencentes ao Greenstone Relt Barbacena. Encaixados nas rochas vulcânicas, ocorrem corpos intrusivos de composição gabróica. A faixa de rochas vulcano-sedimentares apresenta-se concordante com o trend regional de outras faixas greenstone semelhantes de direção NE-SW, e é bordejada e intrudida por rochas graníticas (sensu lato) a NW e SE. As feições texturais e as estruturas primárias parcialmente preservadas encontradas nas rochas ultramáficas indicam origem vulcânica para essas rochas. A origem vulcânica dos anfibolitos (metabasaltos) foi inferida com base na granulação fina, na associação com as rochas ultramáficas vulcânicas e na assinatura geoquímica dessas rochas. As rochas gabróicas têm raras texturas primárias local e parcialmente preservadas, apresentando textura cumulática, confirmando sua natureza intrusiva. As rochas vulcânicas e plutônicas encontram-se metamorfisadas em fácies anfibolito ou xisto-verde, ou transicional entre estas fácies. Duas fases de metamorfismo (M), M2a e M2b), e feições deformacionais correlacionadas aos três eventos caracterizados regionalmente, Dn, Dn+l e Dn+2, foram identificadas. As rochas máficas e ultramáficas vulcânicas e plutônicas apresentam composição tholeiítica. A assinatura geoquímica dos metabasaltos é similar a de basaltos MORB e as rochas vulcânicas ultramáficas são claramente komatiíticas Abstract: In the area around ltutinga-Nazareno, Minas Gerais State, at the southeastem limit of São Francisco Craton, there are outcrops of thick successions of volcanic mafic and ultramafic rocks that are the subbject of the present study. This volcano-sedimentary succession is mainly constituted by metabasalts, metakomatiites and minor metassedimentary rocks, and is considered to be part of the Barbacena Greenstone Belt. Intrusive bodies of gabroic composition also occur in the same area. The strip of the volcano-sedimentary rocks is parallel with the regional NE-SW trend in common with other similar greenstone strips in the sorrounding areas. They are bordered and intruded to the NW and SE by granitic rocks (sensu lato). Partially preserved primary structures and textural features indicate a volcanic origin for the ultramafic rocks. A volcanic origin for the amphibolites (metabasalts) was inferred from their fine-grained texture and the c10se spacial relationship with the volcanic ultramafic rocks. The gabroic rocks at times show rare preserved cumulate texture, attesting to their intrusive nature. The volcanic and plutonic rocks were metamorphosed in amphibolite or greenschist facies, or transitional between the two. Two metamorphic phases, MI, M2a and M2b, and some deformational features correlated to the three regionally recognised events, Dn, Dn+1 and Dn+2, were identified. The mafic and ultramafic volcanic and plutonic rocks show tholeiitic composition. The geochemical signature of the metabasalts is similar MORE, and the volcanic ultramafic rocks are c1early komatiitic Mestrado Metalogenese Mestre em Geociências

APA, Harvard, Vancouver, ISO, and other styles

34

Berry, Neil Howard. "The significance of mafic and ultramafic rocks in the crustal development of northern Greece." Thesis, University of Leicester, 1997. http://hdl.handle.net/2381/30450.

Full text

Abstract:

That there are a number of distinct ophiolitic belts separating some of the major tectonic zones of Greece and the eastern Mediterranean is generally well known. These have previously been interpreted as the remnants of back-arc basins, Mesozoic rifts, and supra-subduction zone type ophiolites. However mafic and ultramafic rocks present in the region of the Serbo-Macedonian Massif, northern Greece, do not appear to fit this model, and have generally been neglected in tectonic interpretations. The aim of this study is to determine how these bodies arrived at their current position, what is their true nature, and how do the answers to these questions help in the interpretation of the way that this section of continental crust was assembled. A multidisciplinary approach was taken to this problem. Structural and tectonic measurements and observations led to the conclusion that the main mafic and ultramafic bodies were accreted into the continental crust via a process of subduction accretion. Further to this, the continental crustal material between the main complexes is composed of tectonic melange material and not microcontinental fragments derived from the northern margin of Gondwana. A geochemical investigation of the Vavdos and Volvi Complexes demonstrates that the origin of these generally depleted lithologies was from a plume source, Volvi being thought to be a seamount, and the Vavdos Complex and associated along strike units, thought to be the disrupted remnants of an oceanic plateau. These conclusions have required the re-interpretation of current tectonic models for the region, and a new model is presented at the end of the thesis.

APA, Harvard, Vancouver, ISO, and other styles

35

Yang, Shenghong, and 杨胜洪. "The permian Pobei mafic-ultramafic intrusion (NE Tarim, NW China) and associated sulfide mineralization." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2011. http://hub.hku.hk/bib/B45874219.

Full text

APA, Harvard, Vancouver, ISO, and other styles

36

SCARSI, MARCO. "Faulting, fluid-rock interaction and hydrothermal mineralisation in ultramafic rocks (Voltri Massif, Ligurian Alps)." Doctoral thesis, Università degli studi di Genova, 2018. http://hdl.handle.net/11567/929962.

Full text

Abstract:

This study deals with reverse faults within intensely carbonated metalherzolites, with related gold mineralisations, from the Voltri Massif, and in particular within the Lavagnina Lakes area, in the Gorzente Valley. This area is located in northwest Italy among the municipalities of Casaleggio Boiro, Lerma, Mornese, and Bosio (Alessandria, Italy; GPS coordinates WGS84, 44.600685° N, 8.784286° E). The Voltri Massif is a metaophiolitic complex, which occurs within the Eastern edges of the Ligurian Alps. It is made up of of metaophiolitic rocks associated with metasediments and slices of subcontinental lithospheric mantle. These rocks underwent a complex Alpine tectono-metamorphic evolution, with blueschist- to eclogite- facies peak metamorphism with variable retrogressive overprints. For this study the analysed structures are the upper crustal deformational events (UDC), from late- to post-orogenic linked to the collisional events. These deformational events are linked to different structural regimes, and developed during the late-Alpine to early-Appenine events. The Lavagnina Lakes area is mainly characterised by outcrops of serpentinites, lherzolites, metabasites, metagabbros, lenses of metasediments, and listvenites (in decreasing order of volumetric extension). From a structural point of view, this area is characterised by brittle to brittle-ductile systems of shear zones, with associated carbonates and chalcedony-quartz veins associated with local gold mineralisations. Hydrothermal, carbon-rich fluids permeated the rocks and sustained these deformation stages producing widespread and intense carbonate-rich alteration zones, exclusive meso- and microstructures within carbonates fault zones, called fault pearls, chalcedony shear veins along fault surfaces, widespread quartzchalcedony and carbonates veining, and leading to local gold mineralisation. The geological survey allowed identifying four main structures (Chapter 5) that I studied in detail. In particular I studied the Bisciarelle Creek thrust fault for the occurrence of meso- and microstructures never reported in literature, called fault pearls. Their compositional and textural characteristics, described in chapter 5.3.4, make the fault core of the Bisciarelle fault a peculiar geological object. 2 The data shown in chapter 7 provide constraints on the chemical properties of the fluid that generate the intense carbonation along the Bisciarelle fault. Through the mass transfer profiles was possible to identify and quantify those elements transferred from the fluid to the rock and vice versa. The morphometric image analysis results (Described in chapter 5.3.5) show that the fault pearls have circular shape irrespective to the direction of observation (parallel and orthogonal to the slickenlines), with values that indicate a nearly perfect circular shape. These values are in line with the roundness values, hence the fault pearls in three-dimensions can be considered as nearly perfect spheres or as very spherical textures. Single-spot SEM-EDS (Chapter 8) analyses show that ferroan dolomite makes the pearl bands (CaO: 29.13±2.33 wt%; MgO: 19.03±4.86 wt%; FeO: 1.77±0.87 wt%) and that minor compositional variations across large and thin bands exist, and that silica makes most of the chalcedony veins (SiO2: 97.97±3.23 wt%). Elemental imaging by LA-ICPTOFMS (Chapter 8) provides a detailed account of the distribution of chemical elements within pearls, matrix, and chalcedony shear veins. Mineral paragenesis and elemental imaging by LA-ICP-TOFMS confirm the hypothesis of hydrothermal derivation of the fault rock. This is best evaluated by comparing the concentration ranges of the key trace elements As, Sb, In, Ga, Ag, Zn, and Cu of fault pearls levels and chalcedony with those of the same elements in the average upper crust. Such comparison clearly shows that the peak concentrations of these elements are 5 (Cu, Zn) to 50 (Sb, In) times higher than those of the upper crust, demonstrating that the Bisciarelle fault fluid was capable to transport and deposit a suite of ore elements. These evidences are fundamental to discuss the possible origin of the fluids that developed the carbonation and the fluid-rock interactions along the Bisciarelle thrust fault and along the main fault of the Lavagnina Lakes area. On the basis of all the constraints described, the fault pearl features are compatible with a genesis from a process called “transient” boiling in microfluidics. This process occurs within cavities when a liquid is instantaneously overheated and a vapour phase nucleates and expands up to explosive boiling, and so generates a myriad of vapour bubbles. Such process, which occurred during mixed mode fracturing in the fault, implies that pearls might reflect the liquid-vapour 3 fractionation of chemical elements in a boiling hydrothermal fluid during seismic failure. The close association of fault pearls with seismic-related structures such as submicron carbonates coating of slip surfaces, quartz microtexture related to silica gel deposition, syn-kinematic filamentous phase, injection veins with similar characteristics and overpressure with respect to seismic pseudotachylites along slip zone supports the hypothesis that fault pearls developed during shear events at seismic rates, and hence are considerable as paleo-seismic events indicators. Moreover I discuss the tectonic evolution of the Lavagnina Lakes area linked to the syn-kynematic fluid rock interaction, the origin of the fluids and the gold mineralisations of the area. The occurrence of syn-tectonic fluid flow and consequent fluid-rock interaction (e.g. carbonation) along the two systems of Reverse Shear Zones (RSZ1-RSZ2), is testified by: metasomatic alteration (ALT-1, ALT-2, and ALT-3), at least three main systems of veins (V1, V2, and V3), and hydraulic and cockade breccias. The evidence that the carbonation took place along these structures, in particular along the RSZs systems, and within their damage zones, highlights how these structures acted as important fluid pathways and played a major control in the distribution of the ore deposits. Finally, I stress out further consideration about the comparison between the gold mineralisations of the area with the gold mineralisations of the whole Voltri Massif.

APA, Harvard, Vancouver, ISO, and other styles

37

Tabit, Adelhalim. "Equilibre orthopyroxene-spinelle : etude experimentale et theorique, application aux roches issues du manteau superieur." Clermont-Ferrand 2, 1986. http://www.theses.fr/1986CLF21025.

Full text

Abstract:

Le travail concerne l'equilibre orthopyroxene-spinelle dans les lherzolites a spinelle, roches caracteristiques du manteau superieur. L'etude mineralogique d'echantillons naturels montre que les teneurs en aluminium et en chrome dans l'orthopyroxene varient avec la texture de l'echantillon, la composition globale du systeme et les conditions de temperature controlant les phases de deformation cristallisation. Le comportement des elements di- et triavalents dans l'equilibre orthopyroxene-spinelle peut etre utilise a des fins geovelocimetriques. Les resultats obtenus lors de l'etude experimentale du systeme simplifie cr::(2)o::(3)-mgo-al::(2)o::(3)-sio::(2) ont fait l'objet d'un traitement mathematique par methode d'inversion generalisee. On obtient ainsi une equation geothermometrique applicable aux roches ultrabasiques du facies lherzolite a spinelle: t4(k)=(61490-16000(y::(crsp))**(2))/(27-8,314lnkd)

APA, Harvard, Vancouver, ISO, and other styles

38

Ilha, Lenon Melo [UNESP]. "Levantamento magnetométrico em sequência metaultramáfica mineralizada em cromita, São Sepé (RS)." Universidade Estadual Paulista (UNESP), 2017. http://hdl.handle.net/11449/151374.

Full text

Abstract:

Submitted by LENON MELO ILHA null (lenonilha@unipampa.edu.br) on 2017-08-22T14:11:00Z No. of bitstreams: 1 Levantamento Magnetométrico em Sequência Metaultramáfica Mineralizada em Cromita, São Sepé (RS).pdf: 4941337 bytes, checksum: 4bae6be70b020d210ee384046ccfeadd (MD5) Approved for entry into archive by Monique Sasaki (sayumi_sasaki@hotmail.com) on 2017-08-23T18:49:11Z (GMT) No. of bitstreams: 1 ilha_lm_me_rcla.pdf: 4941337 bytes, checksum: 4bae6be70b020d210ee384046ccfeadd (MD5) Made available in DSpace on 2017-08-23T18:49:11Z (GMT). No. of bitstreams: 1 ilha_lm_me_rcla.pdf: 4941337 bytes, checksum: 4bae6be70b020d210ee384046ccfeadd (MD5) Previous issue date: 2017-06-30 Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Estudos de prospecção e pesquisa mineral por meio da geofísica são fundamentais para o reconhecimento e incorporação de novas reservas, devido ao baixo custo em relação aos métodos diretos de investigação e a possibilidade de cobertura de amplas áreas. Este trabalho consiste na aplicação do método da Magnetometria Terrestre, na caracterização de um corpo ultramáfico metamorfizado e mineralizado em cromo, a área de estudo se localiza na zona rural do município de São Sepé (RS) e situada nos limites das rochas do Escudo Sul Riograndense. Os litotipos presentes na área são arenitos, rochas metavulcânicas e rochas máficas/ultramáficas. Foram realizadas 1677 leituras em linhas perpendiculares a direção principal do corpo ultramáfico, com espaçamento de 25 metros entre pontos de medida. Os mapas magnetométricos gerados revelam anomalias de alta intensidade, acima de 420nT no mapa de intensidade de campo total, relacionadas com as rochas ultramáficas. Os resultados demonstraram a aplicabilidade do método da magnetometria na individualização de ocorrências minerais magnéticas de dimensões métricas, e a possibilidade de uso na seleção de alvos para perfuração, amostragem e quantificação de teores, em rotinas de pesquisas por depósitos de cromo. Studies of mineral research and exploration through geophysics are fundamental for the recognition and incorporation of new reserves, due to the low cost in relation to the direct methods of investigation and the possibility of covering large areas. This work consists of the application of the Terrestrial Magnetometry method, in the characterization of a metamorphic and mineralized chrome mineralized body, the study area is located in the rural area of the city of São Sepé (RS) and located in the limits of the rocks of the Escudo Sul Riograndense. The lithotypes present in the area are sandstones, metavulcanic rocks and mafic / ultramafic rocks. There were 1677 readings in lines perpendicular to the main direction of the ultramafic body, with spacing of 25 meters between measurement points. The generated magnetometric maps show high intensity anomalies, above 420nT in the map of total field strength, related to ultramafic rocks. The results demonstrated the applicability of the magnetometry method in the individualization of magnetic mineral occurrences of metric dimensions, and the possibility of use in the selection of targets for drilling, sampling and quantification of contents, in search routines for chromium deposits. CNPq: 470821/2013

APA, Harvard, Vancouver, ISO, and other styles

39

Toledo, Catarina Laboure Benfica. "Evolução geologica das rochas maficas e ultramaficas no Greenstone Belt Barbacena, região de Nazareno, MG." [s.n.], 2002. http://repositorio.unicamp.br/jspui/handle/REPOSIP/287167.

Full text

Abstract:

Orientadores : Asit Choudhuri, Gergely Andres Julio Szabo Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Geociencias Made available in DSpace on 2018-08-02T18:21:15Z (GMT). No. of bitstreams: 1 Toledo_CatarinaLaboureBenfica_D.pdf: 10812273 bytes, checksum: 5bada7426b34c70a3319c52bd4bdf6e9 (MD5) Previous issue date: 2002 Resumo: A região de Nazareno está localizada na borda meridional do Cráton do São Francisco e inclui rochas de origem plutônica, vulcânica e sedimentar, arqueanas a mesoproterozóicas, retrabalhadas por eventos termo-tectônicos subseqüentes. Dois conjuntos distintos de rochas máficas e ultramáficas ocorrem nesta região. O primeiro representado por metavulcânicas de filiação komatiítica e toleítica, pertencentes ao Greenstone Belt Barbacena, e o segundo caracterizado por corpos máfico-ultramáficos diferenciados encaixados nessa sucessão vulcano-sedimentar. O presente estudo pretende caracterizar e reconstruir a história evolutiva desses conjuntos de rochas máficas e ultramáficas. As rochas pertencentes à sucessão vulcano-sedimentar estão distribuídas em duas faixas irregulares com direção NE-SW, Faixa Nazareno e Faixa Rio das Mortes, delimitadas por granitóides paleoproterozóicos intrusivos. As rochas de filiação komatiítica são depletadas em alumínio e apresentam características químicas semelhantes às ocorrências clássicas de komatiitos do tipo ADK, com valores de AlzOj/ Ti02 < 20, razões entre Ti, Zr, Sc distintas das razões condríticas e depleção de ETR pesados, sugerindo uma origem a partir de plumas mantélicas profundas, geradas entre 450 e 650 km. As rochas de filiação toleítica apresentam características transicionais entre E-MORB e N-MORB e são semelhantes aos basaltos de plateaus oceânicos, formados por plumas mantélicas em ambiente intraplaca. Associados às faixas vulcano-sedimentares ocorrem quatro corpos máfico-ultramáficos diferenciados, lenticulares e isolados, que apresentam proporções variáveis de termos máficos (metagabros e anfibolitos) e ultramáficos (metaperidotito e metapiroxenito). Apesar do metamorfismo e deformação, as feições texturais originais indicativas de protólitos magmáticos plutônicos diferenciados, tais como texturas cumuláticas e acamamento ígneo, encontram-se ainda preservadas. Os padrões de ETR destes corpos são semelhantes aos dos complexos estratiformes clássicos, sugerindo cristalização em ambiente anorogênico. A região foi afetada por pelo menos três eventos termo-tectônicos, Dn.h Dn e D n+!' O mais antigo, possivelmente arqueano, desenvolveu-se em condições de fácies anfibolito inferior (M)) e seus registros estão impressos nas rochas da sucessão vulcano-sedimentar. O evento de deformação principal (Dn) gerou as feições tectônicas penetrativas da área, registradas tanto na sucessão vulcânica quanto nos corpos mafico-ultramáficos diferenciados. Este evento se processou em condições de fácies anfibolito inferior a médio (M2) e representa a primeira manifestação do Evento Transamazônico na região. A fase Dn+) afetou todas as rochas da região e se desenvolveu em condições de fácies xisto verde superior (Mj). Ela pode representar a segunda manifestação do Evento Transamazônico ou estar relacionada à Orogênese Brasiliana. A evolução geológica proposta para essas rochas envolve a deposição da sucessão vulcano-sedimentar em ambiente de plateau oceânico; colagem e acresção desse plateau em uma margem continental; intrusão de corpos máfico-ultramáficos em ambiente anorogênico; deformação e metamorfismo dessas seqüências durante o Evento Transamazônico, acompanhado pela intrusão de vários corpos granitóides e dioritos associados ao magmatismo do Cinturão Mineiro; e reativação de estruturas mais antigas durante o Evento Brasiliano. A idade do ponto de partida desta evolução ainda não está definida, visto que não existem dados geocronológicos acerca da sucessão vulcano-sedimentar. A idade mínima é balizada pela idade do Trondhjemito Cassiterita (2.162 :I: 10 Ma), intrusivo nos corpos máficoultramáficos e em suas encaixantes Abstract: The study area is located at the southem border of the São Francisco Craton and shows plutonic, vo1canic and sedimentary rocks, of Archean to Mesoproterozoic age, reworked by later thermo-tectonic events. Two different groups of mafic and ultramafic rocks occur in this region. The first is a komatiite-tholeiite sequence belonging to the Barbacena Greenstone Belt, and the second consists of differentiated mafic-ultramafic bodies intruded in this vo1canic-sedimentary sequence. This research aims to characterize and reconstruct the evolution of these two groups of mafic and ultramafic rocks. The rocks ofthe vo1canic-sedimentary sequence are distributed in two irregular NE-SW belts, named Nazareno and Rio das Mortes belts, surrounded by intrusive Paleoproterozoic granitoids. The Al-depleted komatiites (ADK, AlzO3/ TiOz < 20) present Ti, Zr, Sc ratios different from the chondrite pattems and are HREE depleted. They are interpreted as the result of plume related magmatism generated at depths of 450 to 600 km. The tholeiite succession presents transitional characteristic between E-MORB and N-MORB, similar to basalts of oceanic plateau, and is best interpreted as the result of a mantle plume related intra-oceanic plate. Four different mafic-ultramafic layered bodies are distributed in the vo1canic sedimentary belts with different proportions ofmafic (metagabbros and anphibolites) and ultramafic (metaperidotite and metapiroxenite) components. In spite of the metarnorphism and deformation, the original textural features such as cumulate textures and magmatic layering, indicative of differentiated magmatic plutonic protholiths, are still preserved in some of them. The REE pattems ofthese bodies are similar to the classicallayered complex, suggesting an anorogenic setting. The region was affected by at least three thermo-tectonic events, DO-i> Do e D 0+1. The oldest, probably of Archean age, developed at lower amphibolite conditions (M1) is recognizable in the vo1canic sedimentary rocks. Pervasive tectonic features recorded also in the vo1canic sucession and in the mafic-ultramafic layered bodies, characterize the main deformation event Dn. This event occurs in lower to middle amphibolite facies and represents the first register of the Transamazonian Event in the region. The Dn+ 1 phase is impressed in all rocks of the study area and developed at upper greenschist facies (M3), representing either the second manifestation oftheTransamazonian Event or an event related to the Brasiliano Orogenic Cycle. The geological evolution proposed for these rocks involves the deposition ofvo1cano-sedimentary succession in an oceanic plateau setting; collage and accretion of oceanic plateau at a continental margin; intrusion ofmafic-ultrarnafic layered bodies in an anorogenic setting; deformation and metamorphism of these sequences during the Transamazonian event, followed by the intrusion of several granitoid bodies and diorites associated to magmatism of the Mineiro Belt. Probably, the reactivation of the oldest structures in greenschist facies occurred during the Brasiliano Event. The age of the beginning of this evolution is still poorly known. However, the minimum age is marked by the Cassiterite Trondhjemite body (2.612:!: 10 Ma) intrusive in the mafic-ultramafic bodies and their host rocks Doutorado Doutor em Ciências

APA, Harvard, Vancouver, ISO, and other styles

40

Koksal(toksoy), Fatma. "Petrology Of The Phlogopite-bearing Ultramafic-mafic Plutonic Rocks Within Central Anatolian Crystalline Complex, Turkey." Phd thesis, METU, 2003. http://etd.lib.metu.edu.tr/upload/4/655178/index.pdf.

Full text

Abstract:

The aim of this study is to define mineralogical and geochemical characteristics of phlogopite-pargasite enriched ultramafic-mafic cumulate rocks from Kuran&ccedil ali (Kirsehir) and their implications for petrology and regional geological setting. The Kuran&ccedil ali rocks, found within an allochthonous sliver, are representative for the isolated members of the Central Anatolian Ophiolites, derived from closure of Izmir-Ankara-Erzincan branch of Alpine Neotethys. The rocks overthrust the Metamorphic Ophiolitic M&eacute lange (the uppermost part of the Central Anatolian Metamorphics) and cut by felsic dykes of the Late Cretaceous Central Anatolian Granitoids. The Kuran&ccedil ali rocks are unusually enriched in phlogopite and pargasite with varying crystal sizes. They are also composed of diopsidic augite, plagioclase, rutile, ilmenite, sphene, apatite and pyrite. The rocks are divided into six types clinopyroxenite, clinopyroxenite-with-hydrous minerals-plagioclase, phlogopitite, hornblendite, layered gabbro and diorite. Evaluation of detailed EMP data from constituent minerals of different rock types showed that phlogopite with high Fe2+-Fe3+-Al[6]-Ti, diopsidic-augite with high Ca-Al(t)-Ti, Si-undersaturated pargasite with high Al[4]-K-Na-Ti-contents and intercumulus plagioclase with a wide range of composition (an%=40.61-98.58) display unusual compositions. Substitution mechanisms and elemental variations of the minerals suggest crystallization from hydrous metasomatized mantle, high water pressure and oxygen fugacities during formation of the Kuran&ccedil ali rocks. Major oxide, trace and rare earth element abundances of the rock units were used to evaluate petrological characteristics. Chemical and tectonic discrimination diagrams, and parallel multi-element and REE patterns with highly enriched in LILE and LREE relative to HREE and HFSE show strong calc-alkaline affinity with slight alkaline features. Troughs at Nb-Ta and Ti characterize the rocks but these elements are slightly enriched than N-MORB. The rocks show high LREE/HREE ratios. Both unusual mineralogical and geochemical features of the rocks show that the rocks were generated in an arc environment. Moreover, they require a mantle wedge source strongly influenced by metasomatic components (fluid/melt) derived from subducting slab and/or OIB-like alkaline melt. Comparison of the rocks with tectonically well-defined rocks displays that they are generated in an intra-oceanic arc environment, but owe a comparison with fore-arc back-arc Central Anatolian Ophiolites within supra-subduction zone environment revealed that Kuran&ccedil ali rocks are different and generated in an arc basement.

APA, Harvard, Vancouver, ISO, and other styles

41

Toffolo, Luca. "The Cogne magnetite deposit (Western Alps, Italy): a Late Jurassic seafloor ultramafic-hosted hydrothermal system?" Doctoral thesis, Università degli studi di Padova, 2017. http://hdl.handle.net/11577/3422759.

Full text

Abstract:

The Cogne magnetite deposit (Western Alps, Italy) is the largest in a series of apatite and sulphide-free magnetite orebodies that are hosted in serpentinites belonging to western Alpine ophiolitic units. The nearly endmember composition of magnetite, which is unusual for an ultramafic setting, and the relatively high tonnage of the deposit (18 ∙ 10^6 tons at 45-50 wt% Fe) make Cogne an intriguing case study to explore magnetite-forming processes in ophiolites. The Cogne magnetite shows variable textures, including nodular ores, veins and fine-grained disseminations in serpentinites after mantle peridotites and totally serpentinized melt-impregnated peridotites (troctolites). An increase in Co/Ni ratio from magnetite-poor serpentinized peridotites (0.05) to nodular ores (>1) is observed. Trace element analyses of magnetite from different sites and lithologies by laser ablation inductively coupled plasma mass spectrometry indicate that magnetites have typically hydrothermal compositions, characterized by high Mg and Mn (median values up to ~24100 and ~5000 ppm, respectively), and low Cr, Ti and V (median values up to ~30, ~570 and ~60 ppm, respectively). Moreover, the variations in trace element compositions distinguish magnetite that has hydrothermal fluid-controlled composition [highest (Mg, Mn, Co, Zn)/Ni ratios] from magnetite whose composition is affected by host-rock chemistry (highest Ni ± Ti ± V). U-Th-Pb dating of magnetite-associated uraninite constrains the formation of the deposit to the Late Jurassic (ca. 150 Ma), during an advanced stage of the opening of the Alpine Tethys. Thermodynamic modelling of fluid-rock interactions indicates that fluids produced by seawater–peridotite or seawater–Fe-gabbro are not sufficiently Fe-rich to account for the formation of the Cogne deposit. This suggests that fractionation processes such as phase separation were critical to generate hydrothermal fluids capable to precipitate large amounts of magnetite in various types of ultramafic host-rocks. The oceanic setting and geochemical and mineralogical similarities with some modern ultramafic-hosted volcanogenic massive sulphide deposits on mid-ocean ridges suggest that the exposed mineralized section at Cogne may represent the deep segment of a seafloor, high-temperature (~300–400°C) hydrothermal system. The occurrence of similar magnetite enrichments in present-day oceanic settings could contribute to explain the presence of significant magnetic anomalies centred on active and inactive ultramafic-hosted hydrothermal fields. Il giacimento di magnetite di Cogne (Alpi Occidentali, Italia) è il più grande tra le mineralizzazioni a magnetite prive di apatite e solfuri che sono ospitate nelle serpentiniti appartenenti alle unità ofiolitiche delle Alpi Occidentali. La magnetite di composizione prossima al termine puro, insolita in rocce ultramafiche, e il tonnellaggio significativo del giacimento (18 ∙ 10^6 tonnellate con concentrazioni di Fe del 45-50% in peso), rendono Cogne un interessante caso studio per indagare i processi responsabili della formazione di magnetite nelle ofioliti. La magnetite di Cogne si presenta come minerale nodulare, vene e disseminazioni in serpentiniti derivanti da peridotiti di mantello e in peridotiti impregnate da fuso (troctoliti) totalmente serpentinizzate. Il rapporto Co/Ni aumenta a partire dalle serpentiniti povere in magnetite (0.05) fino al minerale nodulare (>1). L'analisi degli elementi in traccia nella magnetite proveniente da differenti siti e litologie, ottenuta tramite laser ablation inductively coupled plasma mass spectrometry, indica che la magnetite ha una composizione tipicamente idrotermale, caratterizzata da alte concentrazioni di Mg e Mn (valori mediani fino a ~24100 e ~5000 ppm, rispettivamente) e bassi Cr, Ti e V (valori mediani fino a ~30, ~570 e ~60 ppm, rispettivamente). Inoltre, le variazioni nel contenuto di elementi in traccia distinguono la magnetite che ha una composizione controllata dal fluido idrotermale [alti rapporti (Mg, Mn, Co, Zn)/Ni] dalla magnetite la cui composizione risente della geochimica della roccia incassante (alti Ni ± Ti ± V). La datazione radiometrica con il metodo U-Th-Pb dell'uraninite associata alla magnetite vincola l'età della formazione del giacimento al Giurassico superiore (circa 150 Ma), durante uno stadio avanzato dell'apertura della Tetide alpina. La modellazione termodinamica delle interazioni fluido-roccia indica che i fluidi risultanti dalle reazioni acqua marina-peridotite e acqua marina-Fe-gabbro non sono sufficientemente ricchi in Fe per generare il giacimento di Cogne. Ciò suggerisce che processi di frazionamento, come la separazione di fase, furono di cruciale importanza per produrre fluidi idrotermali in grado di precipitare grandi quantità di magnetite in varie tipologie di rocce incassanti ultramafiche. Il contesto oceanico e le somiglianze geochimiche e mineralogiche con alcuni moderni depositi vucanogenici a solfuri massivi di dorsale oceanica ospitati in ultramafiti suggeriscono che la sezione mineralizzata di Cogne possa rappresentare il segmento profondo di un sistema idrotermale di fondale oceanico di alta temperatura (~300-400°C). La presenza di analoghe concentrazioni di magnetite nella litosfera oceanica attuale potrebbe contribuire a spiegare l'esistenza di significative anomalie magnetiche situate in corrispondenza di sistemi idrotermali idrotermali sia attivi che inattivi impostati su rocce ultramafiche.

APA, Harvard, Vancouver, ISO, and other styles

42

Giorgetti, Giulia. "Analisi petrografica delle ultramafiti del Passo Val Clapa (Austroalpino superiore, Alta Val di Non)." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2015. http://amslaurea.unibo.it/9171/.

Full text

Abstract:

Questo elaborato ha come obiettivo l'analisi petrografica di rocce ultramafiche facenti parte del basamento metamorfico cristallino affiorante in Alta Val di Non (Provincia autonoma di Trento). Tali rocce appartengono all'Unità di Ultimo (Falda del Tonale, Austroalpino superiore), caratterizzata da corpi ultramafici che affiorano al contatto tra i sottostanti paragneiss a granato e cianite e le soprastanti migmatiti. Il metamorfismo e l'anatessi registrati dalle rocce dell'Unità di Ultimo hanno età Ercinica (Carbonifero Sup.). Lo studio si è concentrato su un corpo ultramafico situato in Alta Val di Bresimo, in località Passo Val Clapa, costituito da una lente di harzburgite a granato attraversato da livelli di olivin-websterite a granato e anfibolo. L'harzburgite è costituita al 65% da olivina, al 20% da serpentino (cresciuto a spese dell'olivina) e al 15% da ortopirosseno; sono presenti spinelli e clinopirosseni accessori. Nel campione analizzato, il granato è sostituito da aggregati policristallini costituiti da kelifite e da anfibolo secondario. La websterite è costituita al 40% da pirosseni (orto e clinopirosseni in uguale quantità), al 25% da anfibolo primario, al 25% da granato, al 5% da olivina e al 5% da minerali opachi. Sono presenti strutture coronitiche attorno ai granati (costituite da kelifite e anfibolo); si nota clorite cresciuta a spese di anfibolo e pirosseni e hyddingsite cresciuta a spese dell'olivina. L'olivin-websterite mostra gli stessi minerali indice riscontrati nell'harzburgite ospitante, segno che entrambi i corpi hanno seguito la medesima evoluzione P-T. In una prima fase la pirossenite si trovava, come la peridotite, in facies a spinello: ciò è confermato dalla presenza di spinelli relitti al nucleo dei granati. Questi ultimi si sono formati a spese dello spinello durante l'aumento di P, una volta superata la soglia di transizione tra le due facies. Le corone kelifitiche, presenti sia nella harzburgite che nella olivin-websterite, rappresentano un'evidenza di metamorfismo retrogrado.

APA, Harvard, Vancouver, ISO, and other styles

43

Farough, Aida. "An experimental study on characterization of physical properties of ultramafic rocks and controls on evolution of fracture permeability during serpentinization at hydrothermal conditions." Diss., Virginia Tech, 2015. http://hdl.handle.net/10919/76669.

Full text

Abstract:

Serpentinization is a complex set of hydration reactions, where olivine and pyroxene are replaced by serpentine, magnetite, brucite, talc and carbonate minerals. Serpentinization reactions alter chemical, mechanical, magnetic, seismic, and hydraulic properties of the crust. To understand the complicated nature of serpentinization and the linkages between physical and chemical changes during the reactions, I performed flow-through laboratory experiments on cylindrically cored samples of ultramafic rocks. Each core had a well-mated through-going tensile fracture, to investigate evolution of fracture permeability during serpentinization. The samples were tested in a triaxial loading machine at an effective pressure of 30 MPa, and temperature of 260°C, simulating a depth of 2 km under hydrostatic conditions. Fracture permeability decreased by one to two orders of magnitude during the 200 to 340 hour experiments. Electron microprobe and SEM data indicated the formation of needle-shaped crystals of serpentine composition along the walls of the fracture, and chemical analyses of sampled pore fluids were consistent with dissolution of ferro-magnesian minerals. The rate of transformation of olivine to serpentine in a tensile fracture is calculated using the data on evolution of fracture permeability assuming the fracture permeability could be represented by parallel plates. Assuming the dissolution and precipitation reactions occur simultaneously; the rate of transformation at the beginning of the experiments was ~ 10-8-10-9 (mol/m2s) and decreased monotonically by about an order of magnitude towards the end of the experiment. Results show that dissolution and precipitation is the main mechanism contributing to the reduction in fracture aperture. The experimental results suggest that the fracture network in long-lived hydrothermal circulation systems may be sealed rapidly as a result of mineral precipitation, and generation of new permeability resulting from a combination of tectonic and crystallization-induced stresses may be required to maintain fluid circulation. Another set of flow through experiments were performed on intact samples of ultramafic rocks at room temperature and effective pressures of 10, 20 and 30 MPa to estimate the pressure dependency of intact permeability. Porosity and density measurements were also performed with the purpose of characterizing these properties of ultramafic rocks. The pressure dependency of the coefficient of matrix permeability of the ultramafic rock samples fell in the range of 0.05-0.14 MPa-1. Using porosity and permeability measurements, the ratio of interconnected porosity to total porosity was estimated to be small and the permeability of the samples was dominantly controlled by microcracks. Using the density and porosity measurements, the degree of alteration of samples was estimated. Samples with high density and pressure dependent permeability had a smaller degree of alteration than those with lower density and pressure dependency. Ph. D.

APA, Harvard, Vancouver, ISO, and other styles

44

Konn, Cécile. "Origin of organic compounds in fluids from ultramafic-hosted hydrothermal vents of the Mid-Atlantic Ridge." Stockholm : Department of Geology and Geochemistry, Stockholm University, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-29172.

Full text

Abstract:

Diss. (sammanfattning) Stockholm : Stockholms universitet, 2009. At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Submitted. Paper 3: Submitted. Paper 4: Submitted.

APA, Harvard, Vancouver, ISO, and other styles

45

Konn, Cécile. "Origin of organic compounds in fluids from ultramafic-hosted hydrothermal vents of the Mid-Atlantic Ridge." Doctoral thesis, Stockholms universitet, Institutionen för geologi och geokemi, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-29172.

Full text

Abstract:

Natural gas, primarily methane (CH4), is produced in substantial amounts in ultramafic-hosted hydrothermal systems. These systems could also generate oil (heavier hydrocarbons) and the first building blocks of life (prebiotic molecules). In the presence of iron bearing minerals, serpentinisation reactions generate H2. Subsequently, CH4 could be synthesised by Fischer-Tropsch Type (FTT) reaction (4H2 + CO2 → CH4 + 2H2O) which is an abiotic process. This has lead to the idea of abiotic formation of larger organic molecules. Both thermodynamics and laboratory work support this idea, yet field data have been lacking. This study focuses on determining the organic content of fluids from ultramafic-hosted hydrothermal systems from the Mid-Atlantic Ridge (MAR) and the origin of the compounds. Fluids were collected from the Lost City, Rainbow, Ashadze and Logatchev vent fields during the EXOMAR (2005), SERPENTINE (2007), MoMARDREAMnaut (2007) and MOMAR08-Leg2 (2008) cruises conducted by IFREMER, France. A SBSE-TD-GC-MS technique was developed and used to extract, concentrate, separate and identify compounds in the fluids. Hydrothermally derived compounds appeared to consist mainly of hydrocarbons and O-bearing molecules. In addition, some amino acids were detected in the fluids by ULPC-ESI-QToF-MS but their origin will need to be determined. The organic content of the Rainbow fluids did not show intra field variability unlike differences could be noted over the years. In order to address the question of the source of the molecules, compound specific carbon isotopic analyses were carried out and completed with a bacterial (Pyrococcus abyssi) hydrothermal degradation experiment. The δ13C data fall in the range of -40 to -30‰ (vs. V-PDB), but individual δ13C values preclude the identification of a biogenic or abiogenic origin of the compounds. The degradation experiment, however, suggests an abiogenic origin of a portion of saturated hydrocarbons whereas carboxylic acids would be biogenic, and aromatic compounds would be thermogenic. At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Submitted. Paper 3: Submitted. Paper 4: Submitted. MoMARnet

APA, Harvard, Vancouver, ISO, and other styles

46

Stewart, Andrew J. "The geochemistry and physical volcanology of the East Lake ultramafic zone, Cape Smith belt, northern Québec /." Thesis, McGill University, 2002. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=29575.

Full text

Abstract:

The East Lake Zone is located within the Raglan horizon of the Cape Smith Foldbelt and hosts an ultramafic dyke/sill complex. The ultramafic units intrude both Raglan horizon siltstone as well as volcanic and volcaniclastic rocks of the Povungnituk Group. Magnesium, silica and chromium variation along with analyses of fresh olivine grains from the East Lake Zone indicate the ultramafic rocks were formed by olivine and chromite accumulation in a magma containing 11--13 wt % MgO. Rare Earth Element profiles of intrusive margins and some Chukotat Group pyroxene-phyric basalts show Light Rare Earth Element enrichment consistent with contamination by Raglan siltstone, however the enrichment occurs stratigraphically below the siltstone, reducing the likelihood of contamination having occurred locally. Sulphur concentrations and olivine nickel contents indicate that minor amounts of sulphide liquid (<0.5%) were present during emplacement. Previous studies have proposed a model for Raglan ultramafic unit contamination and sulphide saturation by thermal erosion of sulphidic sediments by flowing lava. The current study excludes thermal erosion by flowing lava as a mode of contamination and sulphide production as the East Lake Zone units are intrusive, and already have been contaminated and carry a sulphide phase.

APA, Harvard, Vancouver, ISO, and other styles

47

Gao, Jianfeng, and 高剑峰. "Petrogenesis of permian sulfide-bearing mafic-ultramafic intrusions insoutheast Chinese Altay and east Tianshan, NW China." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2012. http://hub.hku.hk/bib/B49617801.

Full text

Abstract:

The Central Asia Orogenic Belt is one of the largest accretionary orogenic belts in the world. In this belt, many sulfide‐bearing mafic‐ultramafic intrusions occur along faults, including the Kalatongke complex in southeast Chinese Altay and the Huangshandong intrusion in east Tianshan. The Kalatongke complex is a composite body including ~308Ma dioritic intrusion and 287Ma sulfide‐bearing mafic intrusion. The dioritic intrusion consists of biotite‐hornblende gabbro, diorite and quartz diorite. This intrusion was formed from a mixture of an evolved mantle‐derived magma and a crust‐derived adakitic magma combined with fractional crystallization of clinopyroxene, amphibole and plagioclase. The mafic intrusion is dominantly made up of norite in which sulfide ores, including disseminated, massive Ni‐Cu and massive Cu‐rich ores, are hosted. This intrusion was formed from two different pulses of basaltic magmas that had different magma evolution histories. The early magma pulse reached sulfide‐saturation due to minor crustal contamination and a small amount of sulfide (<0.03%) was removed before the emplacement. The evolved magmas then entered a shallow magma chamber and assimilated crustal materials to attain sulfide‐saturation again. Sulfide liquids segregated from the magma to form massive Ni‐Cu and massive Cu‐rich ores through further fractionation and residual silicate melts formed norites. A second pulse of magma underwent removal of <0.02% sulfides with stronger crustal contamination, and re‐attained S‐saturation during the emplacement and became a phenocryst‐laden magma. This magma then intruded the earlier formed massive sulfide ores and norites, forming the disseminated sulfide ores. The Permian Huangshandong mafic‐ultramafic intrusion hosts the largest magmatic sulfide deposit in east Tianshan. It consists of a layered unit of lherzolite, gabbro and diorite and a massive unit of olivine gabbronorite and gabbronorite. Both units formed from siliceous high magnesium basaltic (SHMB) magmas derived from a hydrous, depleted mantle source. The two units of the Huangshandong intrusion formed from magmas that have undergone different processes through the evolution of the magma plumbing system. The early magma pulse gained sulfur‐saturation before the emplacement and small amounts of sulfide (<0.03%) were removed to result in a PGE‐depleted, high‐Mg magma. This magma achieved sulfide‐saturation again in a staging magma chamber through crustal contamination and fractional crystallization of olivine and Cr‐spinel (an AFC process) to form the layered unit. A second magma pulse underwent fractionation of more olivine +/‐ Cr‐spinel but less sulfide (<0.003%) removal before the emplacement and became evolved, PEG‐undepleted and low‐Mg before the injection into the magma chamber. Mixing of the two magmas triggered sulfide‐saturation to form sulfide ores with variable PGE, Ni and Cu compositions. The study suggests that SHMB‐like magmatism, produced by melting of depleted and hydrous mantle source, may be an important feature of orogenic belts. Mafic‐ultramafic intrusions formed from SHMB‐like magmas may host economic sulfide deposits, particularly sulfide Ni‐Cu sulfide deposits. published_or_final_version Earth Sciences Doctoral Doctor of Philosophy

APA, Harvard, Vancouver, ISO, and other styles

48

Franchuk, Anatoliy. "HIGH TENOR NI-PGE SULFIDE MINERALIZATION OF THE SOUTH MANASAN ULTRAMAFIC INTRUSION, THOMPSON NICKEL BELT, MANITOBA." Thesis, Laurentian University of Sudbury, 2014. https://zone.biblio.laurentian.ca/dspace/handle/10219/2195.

Full text

Abstract:

The South Manasan ultramafic intrusion (ca. 1880 Ma) located in the Early Proterozoic Thompson Nickel Belt (TNB) contains Ni and platinum group element (PGE) mineralization hosted by disseminated sulfide. Whole-rock Ni values range from 0.3 to 1.7 wt. % and total precious metals (TPMs) range from 0 to 1.3 ppm Pt + Pd + Au and equate to tenor values (i.e., metal in 100% sulfide) of 11-39 wt. % Ni and 8-27 ppm TPMs. The South Manasan intrusion is a steeply dipping sill-like body with a boudinaged outline having a strike length of approximately 1200 m, average width of 125 m and a minimum depth extent of 1000 m. The intrusion is composed of approximately 25% fresh dunite, 50% serpentine altered dunite and 25% tectonized and carbonate altered dunite. The most intense alteration is found near the intrusion’s margin where it is in contact with metasedimentary rocks of the Pipe Formation, part of the surrounding Ospwagan Group. In fresh dunite the sulfide assemblage characterized by an intercumulate texture is dominated by pentlandite with accessory pyrite; the latter having a symplectic-like texture. The pentlandite-pyrite assemblage in the serpentinized dunite, although still characterized overall by an intercumlate-texture, has well developed platy intergrowths with chlorite and serpentine. In the most intensely modified unit (the carbonate altered dunite) the sulfide assemblage consists primarily of pyrrhotite and pentlandite. Whole-rock geochemical data (n=360), modal mineralogy and mineral chemistry obtained on representative drill core throughout the South Manasan intrusion have been used to establish a type section in order to evaluate the relative roles of primary magmatic versus secondary (i.e., serpentinization, carbonate alteration and deformation) processes. These data indicate that the primary silicate-sulfide assemblage was systematically modified during : serpentinization, carbonate alteration and deformation of the South Manasan intrusion such that a sequence of primary versus secondary events can be established. Intrusion of the original komatiitic magma and formation of the South Manasan intrusion took place at a shallow level into consolidated Ospwagan Group sediments with subsequent contamination of this melt with crustal S. This triggered sulfide saturation and generation of an immiscible sulfide melt. Calculated Ni and TPM tenor values constrain the R factor to between 500 and 2500. The early crystallization of olivine inhibited the sulfide melt from settling to the bottom of the magma column and as a consequence, the sulfides now have a primary interstitial magmatic texture. The current sulfide association dominated by pentlandite>>pyrite>chalcopyrite has a mineral paragenesis that is consistent with subsolidus re-equilibration of a primary pentlanditepyrrhotite- chalcopyrite assemblage. The subsequent processes of serpentinization, deformation and carbonate alteration resulted in modifying the primary sulfide assemblages and their textures (i.e., to platy habits), but did not greatly alter the bulk composition, in particular metal contents, except for addition of volatiles (H2O, CO2). It is concluded therefore that the enrichment of the sulfide assemblage at South Manasan in Ni and PGEs is a consequence of a primary magmatic process involving high R factor and that the effects of later overprinting processes (alteration, deformation) are not responsible for the presently observed high-tenor sulfide association.

APA, Harvard, Vancouver, ISO, and other styles

49

Burnham, Oliver Marcus. "The geochemistry of Re and Os in ultramafic rocks from the Pyrenees and Massif Central, France." Thesis, Open University, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.283166.

Full text

APA, Harvard, Vancouver, ISO, and other styles

50

Letsoele, Christopher Sbusiso. "The occurrences of ultramafic pegmatites at Dwarsrivier Mine, Lower Critical Zone, Eastern Bushveld Complex, South Africa." Diss., University of Pretoria, 2017. http://hdl.handle.net/2263/63298.

Full text

Abstract:

This study presents a detailed petrological and geochemical investigation of the concordant ultramafic pegmatites of the Lower Critical Zone at Dwarsrivier Mine, in the eastern Bushveld Complex. The pegmatites are coarse-grained and of variable size and mineralogy. They occur within the LG-6 chromitite layer as well as in the silicate rocks of the Rustenburg Layered Suite. Field observations into their occurrence, and their association with the LG-6 chromitite layer, suggest that the pegmatites intrude, deform and disrupt the LG-6 chromitite. The mineralogy of the pegmatites is similar as the surrounding pyroxenite rocks, although they are texturally different from the surrounding pyroxenite host rocks. They comprise variable amounts of clinopyroxene, orthopyroxene, olivine, plagioclase, biotite and accessory amphiboles. Based on dominant mineralogy, the pegmatites can be grouped into clinopyroxene-, orthopyroxene- and olivine-rich pegmatites. The major and trace element composition of the pegmatites is different from the surrounding pyroxenite host rocks. The whole rock geochemistry of the pegmatites indicate that the pegmatites have a slightly higher concentration of incompatible trace elements compared to the pyroxenite host rocks, although compositional overlaps exist. Whole rock Mg# and trace element ratios suggests that the pegmatites are the products of less fractionated liquid(s) than their surrounding pyroxenite rocks. When the whole rock geochemical data of the pegmatites are compared to other similar concordant pegmatites in the eastern Bushveld Complex, as well as the discordant pegmatites from the western Bushveld Complex, it is established that the pegmatites at Dwarsrivier mine are not genetically related to the discordant, intrusive iron-rich pegmatites. They are also different from the concordant pegmatites found elsewhere in the eastern Bushveld Complex. The pegmatites are interpreted as the products of a volatile-rich melt which promoted the recrystallization or sub-solidus enlargement of the pyroxenes. The occurrence of cumulus olivine at the stratigraphic position of the Lower Critical Zone is exceptional. Olivine crystalized as a result of continuous phase shifts within the pegmatite melt. Some of the pegmatites are serpentinised by late hydrothermal fluids. The olivine-rich pegmatites display the most prominent serpentinisation, and are composed of a mineral assemblage dominated by serpentine and magnetite. Dissertation (MSc)--University of Pretoria, 2017. Assmang Dwarsrivier Mine Geology MSc Unrestricted

APA, Harvard, Vancouver, ISO, and other styles

Dissertations / Theses on the topic 'Ultramafics'

Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles